The concept for Disneyland began when Walt Disney was visiting Griffith Park in Los Angeles with his daughters Diane and Sharon. While watching them ride the merry-go-round, he came up with the idea of a place where adults and their children could go and have fun together, though this idea lay dormant for many years. The earliest documented draft of Disney's plans was sent as a memo to studio production designer Dick Kelsey on August 31, 1948, where it was referred to as a "Mickey Mouse Park", based on notes Disney made during his and Ward Kimball's trip to the Chicago Railroad Fair the same month, with a two-day stop in Henry Ford's Museum and Greenfield Village, a place with attractions like a Main Street and steamboat rides, which he had visited eight years earlier.

When people wrote letters to Disney to inquire about visiting the Walt Disney Studios, he realized that a functional movie studio had little to offer to visiting fans, and began to foster various ideas about building a site near the Burbank studios for tourists to visit. His ideas evolved to a small play park with a boat ride and other themed areas. The initial park concept, the Mickey Mouse Park, was originally planned for a sixteen-acre (6.5 ha) plot to the south, across Riverside Drive from the studio. Besides Greenfield Village and the Chicago Railroad Fair, Disney was also inspired by Tivoli Gardens in Denmark, Knott's Berry Farm, Colonial Williamsburg, the Century of Progress in Chicago, and the New York's World Fair of 1939.

His designers began working on concepts, though the project grew much larger than the land could hold. Disney hired C. V. Wood and Harrison Price of the Stanford Research Institute (SRI) to identify the proper area in which to position the planned theme park based on future population growth. Based on Price's analysis (for which he would be recognized as a Disney Legend in 2003), Disney acquired 160 acres (65 ha) of orange groves and walnut trees in Anaheim, southeast of Los Angeles in neighboring Orange County. The small Burbank site originally considered by Disney is now home to Walt Disney Animation Studios and ABC Studios.

Roy O. Disney hired Wood away from SRI as executive vice president to undertake the task of actually building Disneyland. When Walt told Wood that he wanted a paddle steamer in Disneyland, it was Wood who introduced Walt to his good friend Joe Fowler, a retired U.S. Navy rear admiral. Fowler was then hired by Walt to "make engineering realities out of" all of Walt's ideas, not just a paddle wheeler—in other words, Fowler became the actual "construction boss" of Disneyland, charged with turning Disneyland from Walt's dream into a reality in only one year.

Difficulties in obtaining funding prompted Disney to investigate new methods of fundraising, and he decided to create a show named Disneyland. It was broadcast on then-fledgling ABC. In return, the network agreed to help finance the park. For its first five years of operation, Disneyland was owned by Disneyland, Inc., which was jointly owned by Walt Disney Productions, Walt Disney, Western Publishing and ABC. In addition, Disney rented out many of the shops on Main Street, U.S.A. to outside companies. By 1960, Walt Disney Productions had bought out all other shares, but the partnership had already led to a lasting relationship with ABC which would eventually culminate in the Walt Disney Company's acquisition of ABC in the mid-1990s.

Construction began on July 16, 1954, and cost $17 million to complete (equivalent to $153 million in 2023). The park was opened one year and one day later. U.S. Route 101 (later Interstate 5) was under construction at the same time just north of the site; in preparation for the traffic Disneyland was expected to bring, two more lanes were added to the freeway before the park was finished.

Disneyland was dedicated at an "International Press Preview" event held on Sunday, July 17, 1955, which was open only to invited guests and the media. Although 28,000 people attended the event, only about half of those were invitees, the rest having purchased counterfeit tickets, or snuck into the park by climbing over the fence. The following day, it opened to the public, featuring twenty attractions. The Special Sunday events, including the dedication, were televised nationwide and anchored by three of Walt Disney's friends from Hollywood: Art Linkletter, Bob Cummings, and Ronald Reagan. ABC broadcast the event live, during which many guests tripped over the television camera cables. In Frontierland, a camera caught Cummings kissing a dancer. When Disney started to read the plaque for Tomorrowland, he read partway when an off-camera technician stopped him, and Disney responded, "I thought I got a signal", and began the dedication again. At one point, while in Fantasyland, Linkletter tried to give coverage to Cummings, who was on the pirate ship. He was not ready and tried to give the coverage back to Linkletter, who had lost his microphone. Cummings then did a play-by-play of him trying to find it in front of Mr. Toad's Wild Ride.

Traffic was delayed on the two-lane Harbor Boulevard. Famous figures who were scheduled to show up every two hours showed up all at once. The temperature was an unusually high 101 °F (38 °C), and because of a local plumbers' strike, Disney was given a choice of having working drinking fountains or running toilets. He chose the latter, leaving many drinking fountains dry. This generated negative publicity since Pepsi sponsored the park's opening; disappointed guests believed the inoperable fountains were a cynical way to sell soda, while other vendors ran out of food. The asphalt that had been poured that morning was soft enough to let women's high-heeled shoes sink into it. Some parents threw their children over the crowd's shoulders to get them onto rides, such as the King Arthur Carrousel. In later years, Disney and his 1955 executives referred to July 17, 1955, as "Black Sunday". After the extremely negative press from the preview opening, Walt Disney invited attendees back for a private "second day" to experience Disneyland properly.

At the time, and during the lifetimes of Disney and his brother Roy, July 17 was considered a preview, with July 18 the official opening day. Since then, aided by memories of the television broadcast, the company has adopted July 17 as the official date, the one commemorated every year as Disneyland's birthday.

Within a year after Disneyland's opening, increasing friction between Disney and Wood resulted in Wood's termination. Most of the executives who led the development of Disneyland are now commemorated in window signs as proprietors of fictional businesses along Main Street, USA, with the exception of Wood.

In September 1959, Soviet First Secretary Nikita Khrushchev spent thirteen days in the United States, with two requests: to visit Disneyland and to meet John Wayne, Hollywood's top box-office draw. Due to the Cold War tension and security concerns, he was famously denied an excursion to Disneyland. The Shah of Iran and Empress Farah were invited to Disneyland by Walt Disney in the early 1960s. There was mild controversy over the lack of African American employees. As late as 1963, civil rights group the Congress of Racial Equality, was in discussions with Disneyland officials about hiring more black people, with Disneyland telling the group they would consider their requests. Unlike other amusement parks at the time, Disneyland was never racially segregated, and was open to all races since opening day.

As part of the Casa de Fritos operation at Disneyland, "Doritos" (Spanish for "little golden things") were created at the park to recycle old tortillas that would have been discarded. The Frito-Lay Company saw the popularity of the item and began selling them regionally in 1964, and then nationwide in 1966.

On August 6, 1970, an estimated 300+ anti-war Yippies entered Disneyland in a planned protest against the Vietnam War. The protestors held grievances with specific aspects of the theme park itself, such as the Aunt Jemima-themed pancake restaurant in Frontierland and the park's association with Bank of America, a subject of controversy at the time for its lending to military contractors such as Boeing. The Yippies were met by an estimated 100 riot police who established lookouts within the park and another 300 on standby just outside of the entrance gates. Around 4:00 p.m., many of the Yippies occupied Tom Sawyer Island, purportedly smoking cannabis and causing cast members to halt park guests from boarding rafts to the island. An hour later, the group of Yippies converged at Main Street, U.S.A. and became confrontational with other park guests and riot police after tearing down patriotic bunting while unfurling Viet Cong and Youth International Party flags. Standby riot police entered and the park was evacuated around 5:00 p.m. when some of the insurgents approached the park's Bank of America branch, sparking concern that the building could be burned in a similar fashion to the arson of a Bank of America in Isla Vista in February 1970. Police arrested 23 park guests and it was only the second unexpected early closure in park history, the first being in response to the assassination of John F. Kennedy in 1963. The incident was cited as a clash of the park management's perceived appeal to tradition following the death of Walt Disney and the growing counterculture movement among young people in the United States.

Despite the opening of the more expansive Walt Disney World resort in 1971, Disneyland continued to set attendance records and maintained its status as a major tourist attraction. In 1972, the Bear Country land was opened and the Main Street Electrical Parade was introduced.

Disneyland underwent several changes in preparation for the United States Bicentennial. In 1974, Walt Disney's Carousel of Progress was replaced with America Sings, an audio-animatronic theater show featuring the history of American music. America on Parade debuted in 1975 and ran through 1976 in celebration of the bicentennial.

Several of the park's earliest attractions received major changes or were replaced in the mid-to-late 1970s. The Flight to the Moon attraction was rethemed as Mission to Mars in March 1975, five years after Apollo 11 had successfully landed humans on the Moon. Construction of Space Mountain began that same year adjacent to the new Mission to Mars attraction but was delayed by El Niño-related weather complications. The ride opened in 1977 to much acclaim as lines would often stretch all the way to Main Street, U.S.A. The final major change of the decade came in 1977 when the slow-paced Mine Train Through Nature's Wonderland was closed and replaced by the similarly themed Big Thunder Mountain Railroad rollercoaster in 1979.

Fantasyland was closed for refurbishment in 1982 and reopened to the public in 1983 as "New Fantasyland."

On December 5, 1985, to celebrate Disneyland's 30th year in operation, one million balloons were launched along the streets bordering Disneyland as part of the Skyfest Celebration.

In the late 1990s, work began to expand the one-park, one-hotel property. Disneyland Park, the Disneyland Hotel, the site of the original parking lot, and acquired surrounding properties were earmarked to become part of the Disneyland Resort. At that time, the property saw the addition of the Disney California Adventure theme park, a shopping, dining and entertainment complex named Downtown Disney, a remodeled Disneyland Hotel, the construction of Disney's Grand Californian Hotel & Spa, and the acquisition and re-branding of the Pan Pacific Hotel as Disney's Paradise Pier Hotel (renamed to Pixar Place Hotel in 2024). The park was renamed "Disneyland Park" to distinguish it from the larger complex under construction. Because the existing parking lot (south of Disneyland) was repurposed by these projects, the six-level, 10,250-space Mickey and Friends parking structure was constructed in the northwest corner. Upon completion in 2000, it was the largest parking structure in the United States.

The park's management team during the mid-1990s was a source of controversy among fans and employees. In an effort to boost profits, various changes were begun by then-executives Cynthia Harriss and Paul Pressler. While their initiatives provided a short-term increase in shareholder returns, they drew widespread criticism for their lack of foresight. The retail backgrounds of Harriss and Pressler led to a gradual shift in Disneyland's focus from attractions to merchandising. Outside consultants McKinsey & Company were brought in to help streamline operations, resulting in many changes and cutbacks. After nearly a decade of deferred maintenance, the original park was showing signs of neglect. Fans of the park decried the perceived decline in customer value and park quality and rallied for the dismissal of the management team.

Matt Ouimet, the former president of the Disney Cruise Line, was promoted to assume leadership of the Disneyland Resort in late 2003. Shortly afterward, he selected Greg Emmer as Senior Vice President of Operations. Emmer was a long-time Disney cast member who had worked at Disneyland in his youth prior to moving to Florida and held multiple executive leadership positions at the Walt Disney World Resort. Ouimet set about reversing certain trends, especially concerning cosmetic maintenance and a return to the original infrastructure maintenance schedule, in hopes of restoring Disneyland's former safety record. Similarly to Walt Disney, Ouimet and Emmer could often be seen walking the park during business hours with members of their respective staff, wearing cast member name badges, standing in line for attractions, and welcoming guests' comments. In July 2006, Ouimet left The Walt Disney Company to become president of Starwood. Soon after, Ed Grier, executive managing director of Walt Disney Attractions Japan, was named president of the resort. In October 2009, Grier announced his retirement, and was replaced by George Kalogridis.

The "Happiest Homecoming on Earth" was an eighteen-month-long celebration (held through 2005 and 2006) of the fiftieth anniversary of Disneyland Park, also celebrating Disneyland's milestone throughout Disney parks worldwide. In 2004, the park underwent major renovations in preparation, restoring many attractions, notably Space Mountain, Jungle Cruise, the Haunted Mansion, Pirates of the Caribbean, and Walt Disney's Enchanted Tiki Room. Attractions that had been in the park on opening day had one ride vehicle painted gold, and the park was decorated with fifty Golden Mickey Ears. The celebration started on May 5, 2005, and ended on September 30, 2006, and was followed by the "Year of a Million Dreams" celebration, lasting twenty-seven months and ending on December 31, 2008.

Beginning on January 1, 2010, Disney Parks hosted the Give a Day, Get a Disney Day volunteer program, in which Disney encouraged people to volunteer with a participating charity and receive a free Disney Day at either a Disneyland Resort or Walt Disney World park. On March 9, 2010, Disney announced that it had reached its goal of one million volunteers and ended the promotion to anyone who had not yet registered and signed up for a specific volunteer situation.

In July 2015, Disneyland celebrated its 60th Diamond Celebration anniversary. Disneyland Park introduced the Paint the Night parade and Disneyland Forever fireworks show, and Sleeping Beauty Castle was decorated in diamonds with a large "60" logo. The Diamond Celebration concluded in September 2016 and the whole decoration of the anniversary was removed around Halloween 2016.

Disneyland Park, along with Disney California Adventure, Downtown Disney, and the resort hotels, closed indefinitely starting March 14, 2020, in response to the COVID-19 pandemic. After nearly four months of closure, Downtown Disney reopened on July 9, 2020. The parks had been scheduled to reopen on Disneyland's 65th anniversary on July 17, 2020, but due to rising cases in California, the parks' reopening was once again postponed. It was expected to stay closed until at least December 31, 2020. In February 2021, Disneyland announced a limited-capacity ticketed event called "A Touch of Disney", which would offer guests to shop at stores and enjoy eateries around the park from March 18 through April 19, 2021. On March 5, 2021, it was announced by the California Department of Public Health that Disneyland could reopen with capacity restrictions beginning April 1, 2021. The following week, then-Disney CEO Bob Chapek said that the company was planning on officially reopening the park in late April 2021. Disneyland along with Disney California Adventure officially reopened on April 30, 2021, with limited capacity and social distancing/mask guidelines in effect. On June 15, 2021, Disneyland, Disney California Adventure and other theme parks in California were permitted to return to full capacity with most COVID-19 pandemic restrictions lifted per California governor Gavin Newsom's Blueprint for a Safer Economy phased re-opening. Prior to this, Disneyland was operating at reduced guest capacity since it re-opened on April 30, 2021, after 13 months of closure due to the pandemic.

On March 25, 2021, the company announced a plan titled DisneylandForward to expand the park with more rides, restaurants, and shops with the Anaheim City Council expected to receive the development plans for approval by 2023. The plan was approved by the Anaheim City Council on May 7th, 2024.

On January 27, 2023, Disneyland kicked off the year-long celebration of the centennial of The Walt Disney Company, Disney100. Disneyland Park introduced the Mickey & Minnie's Runaway Railway attraction and Wondrous Journeys fireworks show.

On April 13, 2023, it was announced that Disneyland would be holding its first official "Pride Nite", supporting the LGBTQ community. This comes 25 years after the first celebrated 'Gay Day' at Disneyland, which is identical to the Gay Days at Walt Disney World celebration. In May 2023, a video featuring an employee positioned in Fantasyland at the Bibbidi Bobbidi Boutique as one of the Fairy Godmother's apprentices was published on TikTok, generating both criticism from conservative commentators and support from fans on social media due to the employee being male-presenting.

On May 18, 2024, Disneyland character performers voted to join the Actors' Equity Association, with 79% voting in favor. The decision marked the first time these workers have unionized since Disneyland's opening in 1955.