Union Parish (French: Paroisse de l'Union) is a parish located in the U.S. state of Louisiana. As of the 2010 census, the population was 22,721. The parish seat is Farmerville. The parish was created on March 13, 1839, from a section of Ouachita Parish. Its boundaries have changed four times since then (in 1845, 1846, 1867, and 1873, respectively).