Valleyfair opened on May 25, 1976, featuring 20 rides and attractions on 26 acres (110,000 m2), with the roller coaster High Roller being the main attraction. The carousel in the park came from Excelsior Amusement Park which was closed in 1973. It is the oldest ride in the park. In 1978 in an effort to increase investment capital for continued park expansion, Valleyfair was acquired by Cedar Point in Sandusky, Ohio. Five years later, Cedar Fair Limited Partnership was formed as the parent company for Cedar Point and Valleyfair (the name being derived from the names of both properties). Since 1976, Valleyfair has invested over $96 million into the park, and today the park has over 75 attractions on 90 acres (36 ha) of land.

A height restriction was imposed in 2000 with the building of the Power Tower. After negotiations with the FAA and the nearby Flying Cloud Airport, the FAA restricted the building height of the Power Tower at 275 feet (84 m) due to its proximity to the airport. Power Tower's original plan was to be a height of 300 feet (91 m) and to take riders to 275 feet (84 m).

Valleyfair did not open for the 2020 season because of the COVID-19 pandemic in the United States, although it was reopened for the 2021 season.

On July 1, 2024, a merger of equals between Cedar Fair and Six Flags was completed, creating Six Flags Entertainment Corporation. This officially retired the Cedar Fair branding that was partially derived from Valleyfair.

As the park is located on the banks of the Minnesota River, flooding can become an issue during the springtime months before the park usually opens (or when the park is open for the season), notably in 1988, 1993, 1997, 2014, 2018, 2019, and 2024. Excalibur and Thunder Canyon are built outside of a pre-existing river dike, and were built with this flooding potential in mind.