John Patrick Parnell "Patsy" Cahill (April 4, 1865 – October 31, 1901) was an American Major League Baseball outfielder.

In 1885 Cahill played for the Atlanta ball club of the Southern Association.

On March 8, 1887 Cahill was purchased by the Indianapolis Hoosiers from the St. Louis Maroons.

Cahill would play out his final season in the Major Leagues with the Hoosiers batting .205 with 54 hits, four doubles, three triples, 26 RBIs and a career high 34 steals in 68 games.

In addition to Cahill's batting statistics he also pitched a career high six games, including one start.