Port Arthur is a city in the U.S. state of Texas, 90 mi east of Houston. Part of the Beaumont–Port Arthur metropolitan area, Port Arthur lies primarily in Jefferson County, with a small extension in Orange County. The largest oil refinery in the United States, the Motiva Refinery, is located there. The population of Port Arthur was 53,818 at the 2010 census, down from 57,755 at the 2000 census. By 2020, its population had rebounded to 56,039.