Washington Parish is a parish located in the interior southeast corner of the U.S. state of Louisiana, one of the Florida Parishes. As of the 2020 census, the population was 45,463. Its parish seat is Franklinton. Its largest city is Bogalusa. The parish was founded in 1819. Washington Parish comprises the Bogalusa, LA Micropolitan Statistical Area, which is included in the New Orleans-Metairie-Hammond, LA-MS Combined Statistical Area.