William J. Barker (December 23, 1831 – March 27, 1900) was an American politician who served as the mayor of Denver, Colorado from 1874 to 1876. He was a pioneer and moved to Denver in 1860, buying a large amount of property. 1876, Barker's last year as mayor office, is the same year Colorado was granted statehood.
He is buried in the Fairmount Cemetery.