Ormsby Brunson Thomas (21 August 1832-24 October 1904) was a member of the US House of Representatives (R-WI 7) from 4 March 1885 to 3 March 1891, succeeding Gilbert M. Woodward and preceding Frank P. Coburn. Born in Sandgate, Vermont, he was raised in Prairie du Chien, Wisconsin before becoming a lawyer and serving as the Democratic district attorney of Crawford County from 1858 to 1862. He served in the 31st Wisconsin Infantry Regiment during the American Civil War before serving in the state assembly and becoming a Republican in 1867. He served in Congress from 1885 to 1891, and he died in 1904.