Agricultural Society Fair Grounds was a fairground on the west side of Rockford, Illinois. It served as the grounds for the Winnebago County Agricultural Society. It was used as a baseball grounds by the Rockford Forest Citys baseball club of the National Association during the 1871 season, so it is considered a major league ballpark by those who consider the NA to have been a major league. The Forest Citys had played their home games at the Fair Grounds beginning in 1866, and continued to call it home for the 1871 season.