Sulphur is a city in and county seat of Murray County, Oklahoma, United States. The population was 5,065 at the 2020 census, a 2.8 percent gain over the figure of 4,929 in 2010. The area around Sulphur has been noted for its mineral springs, since well before the city was founded late in the 19th century. The city received its name from the presence of sulfur in the water.