William H. Ahearn (1858 – April 28, 1919) was an American Major League Baseball catcher, at least for one day, during the 1880 season. He was born in Troy, New York.

Ahearn played in one game for the Troy Trojans of the National League on June 19, 1880. Behind the plate, he had two putouts, five assists, and two errors for a fielding percentage of .778. He also had seven passed balls. At the plate, he went 1-for-4 for a .250 batting average, and he scored one run. The Trojans lost the game to the Cleveland Blues 18-6. It was played at Haymakers' Grounds in Troy, New York. Ahearn died in Troy on April 28, 1919.

• Career statistics from Baseball Reference, or Fangraphs
• Baseball Almanac
• Retrosheet