John Reilly Costello (born December 24, 1960 in Bronx, New York) is a former relief pitcher in Major League Baseball who played for the St. Louis Cardinals (1988-1990), Montreal Expos (1990) and San Diego Padres (1991). He batted and threw right-handed.
In a four-season career, Costello posted an 11-6 record with a 2.97 ERA and four saves in 119 games pitched.