Named for the Tulsa Lochapokas indian tribe, the City of Tulsa was incorporated in 1898. The finding of oil in 1901 resulted in rapid growth and still links Tulsa to the US oil industry. The city, with a population of over 395,000, straddles the Arkansas River and maintains a temperate climate. AAON, Mazzios, Nordam Group, ONEOK, and The Williams Companies headquarter in Tulsa. The University of Tulsa, Oral Roberts University, and Rogers State University form the base of the 15 institutions in the city.