The land which became Rainbow Park was homesteaded in 1836 by William Powell and Robert Grignon. Knaggs Ferry operated there from 1831 to 1847, serving as the main cross-river transportation from the Green Bay area until a bridge was built. The city bought the land from Paine Lumber Company in 1937, but the park was not developed until 1948. In 1957 Rainbow Memorial Park was dedicated to the memory of the Oshkosh soldiers who served with the 42nd (Rainbow) Division in World War I, many of whom had spent their boyhood days on the river.
Rainbow Park covers approximately 17 acres with roughly 0.45 miles of shoreline with it being a popular launch spot for boating enthusiasts.