The 1921 Chicago Cardinals season was their second in the American Professional Football Association. The Cardinals failed to improve on their previous output of 6–2–2, winning only three APFA games. They finished eighth in the league.
Although a myth persists that the team billed itself as the "Racine Cardinals", by 1921, the press generally referred to the team as the "Chicago Cardinals" and references to Chris O'Brien's team with the Racine name were few. The team had no connection to Racine, Wisconsin, and played at Normal Park on Chicago's Racine Avenue.