William Pitt Kellogg (December 8, 1830 – August 10, 1918) was an American lawyer and Republican Party politician who served as a United States Senator from 1868 to 1872 and from 1877 to 1883 and as the Governor of Louisiana from 1873 to 1877 during the Reconstruction Era. He was one of the most important politicians in Louisiana during and immediately after Reconstruction, notable for being elected after most other Republican officials had been defeated when white Democrats regained control of state politics.He is also notable as one of few incumbent Senators to be elected to the House of Representatives, where he served from 1883 to 1885. He was the last Republican Governor of Louisiana until Dave Treen in 1980.