William Arthur Karns (December 28, 1875 – November 15, 1941) was a Major League Baseball pitcher.

Karns played for the Baltimore Orioles in 1901.

In 3 career games, he had a 1–0 record, with a 6.35 ERA.

Karns was born in Richmond, Iowa, and died in Seattle, Washington.

This biographical article relating to an American baseball pitcher born in the 1870s is a stub.