William J. Brown (died 1970) was an American architect based in Cedar Rapids in the U.S. state of Iowa. He is also known by his full name, William Jay Brown. William J. Brown studied architecture at the University of Illinois. He worked for prominent architects in Chicago and New York including Holabird & Roche, Kenneth M. Murchison, and John Russell Pope.He and his older brother Frederick G. Brown established the Brown Brothers architectural firm. One of their first projects, in 1910, was the Knights of Pythias Hall, but in 1911 Frederick died. William J. Brown stayed and supervised the completion of the Knights of Pythias Building in 1912.