The first professional baseball team, the 1869 Cincinnati Red Stockings, played their home games on this site in a ballpark called Union Grounds. The facility included a main grandstand (nicknamed the "Grand Duchess"), two wings of bleacher seats down each baseline, and a clubhouse. Seating capacity was approximately 4,000, but as many as 12,000 were estimated to have filled the grounds for important games. The grounds were 550 feet square and were surrounded by a large fence.
Union Grounds opened in 1867 and hosted its first game on July 5th. After the Red Stockings disbanded in 1870, and with the owners of the club facing bankruptcy, the wooden stands and fence were dismantled and sold as scrap in 1872.
The ballpark was bounded by Kenner Street (to the north) and Hopkins Street (to the south). The main grandstand and home plate were located near this landmark and faced the northwest.