William James Patterson (February 7, 1838 – November 6, 1926) was the Commander-in-Chief of the Grand Army of the Republic from 1916 to 1917.

He served in the American Civil War and was wounded and captured at the Battle of Gaines' Mill.

He served as the Pennsylvania's Department Commander of the Grand Army of the Republic from 1898 to 1899.

In May 1913 he was named to an eight-member commission to plan the 50th anniversary commemoration of the Battle of Gettysburg.

He was the Commander-in-Chief of the Grand Army of the Republic from 1916 to 1917.