Purcell is a city in McClain County, Oklahoma, United States, and the county seat. As of the 2010 census, the city population was 5,884.Purcell's railroad heritage includes being named after E.B. Purcell of Manhattan, Kansas, former director of the Atchison, Topeka and Santa Fe Railway (ATSF).Purcell is often called the "Quarterhorse Capital of the World" and its official motto is "Heart of Oklahoma"; the city has registered trademarks on both titles.