William Findlay Coolbaugh (July 1, 1821 – November 13, 1877) was an American politician and banker from Pennsylvania. After working his way up the ranks at a Philadelphia dry goods house, he began his own store in Burlington, Iowa in 1842. He became active in Iowa politics, serving in the Iowa Senate from 1854 to 1862. In 1855, he was the Democratic Party candidate to the United States Senate, but lost. In 1862, he moved to Chicago, Illinois to set up a banking house which became the Union National Bank of Chicago. Coolbaugh was also the father-in-law of Chief Justice of the United States Melville Fuller. Coolbaugh died of an apparent suicide in 1877.