John Nelson Kerins (July 15, 1858 – September 8, 1919), sometimes known as Jack Kerins, was an American Major League Baseball player who appeared mainly at first base but also at catcher and in the outfield. He played for the Indianapolis Hoosiers (1884), Louisville Colonels (1885-1889), Baltimore Orioles (1889) and St. Louis Browns (1890). He was a player-manager for Louisville in 1888 and for St. Louis in 1890, and he umpired American Association games through 1891.