This is lower than the national figure (about 12.5% of U.S. residents were foreign-born). The center of population of Oklahoma is in Lincoln County near the town of Sparks. The state's 2006 per capita personal income ranked 37th at $32,210, though it has the third-fastest-growing per capita income in the nation and ranks consistently among the lowest states in cost of living index. The Oklahoma City suburb Nichols Hills is first on Oklahoma locations by per capita income at $73,661, though Tulsa County holds the highest average. In 2011, 7.0% of Oklahomans were under the age of 5, 24.7% under 18, and 13.7% were 65 or older. Females made up 50.5% of the population. The state is in the U.S. Census' Southern region. According to the 2010 United States Census, Oklahoma is the 28th-most populous state with inhabitants but the 19th-largest by land area spanning of land. Oklahoma is divided into 77 counties and contains 597 incorporated municipalities consisting of cities and towns. In Oklahoma, cities are all those incorporated communities which are 1,000 or more in population and are incorporated as cities. Towns are limited to town board type of municipal government. Cities may choose among aldermanic, mayoral, council-manager, and home-rule charter types of government. Cities may also petition to incorporate as towns. The English language has been official in the state of Oklahoma since 2010. The variety of North American English spoken is called Oklahoma English, and this dialect is quite diverse with its uneven blending of features of North Midland, South Midland, and Southern dialects. In 2000, 2,977,187 Oklahomans—92.6% of the resident population five years or older—spoke only English at home, a decrease from 95% in 1990. 238,732 Oklahoma residents reported speaking a language other than English in the 2000 census, about 7.4% of the state's population. The two most commonly spoken native North American languages are Cherokee and Choctaw with 10,000 Cherokee speakers living within the Cherokee Nation tribal jurisdiction area of eastern Oklahoma, and another 10,000 Choctaw speakers living in the Choctaw Nation directly south of the Cherokees. Cherokee is an official language in the Cherokee Nation tribal jurisdiction area and in the United Keetoowah Band of Cherokee Indians. In addition to Cherokee, more than 25 Native American languages are spoken in Oklahoma, second only to California.