Oklahoma County, also shortened to OKC, is Oklahoma state's capital and biggest city. The county seat of Oklahoma County, the city ranks 27th in population of over 640,000 people among United States cities. Town of Oklahoma has one of the biggest cattle markets in the nation. The primary field of the local economy is shale, natural gas, refined goods, and associated industries. The town is in the center of an active oil field and the capitol grounds are lined with oil derricks. Oklahoma City is located on the I-35 Corridor, one of the most important southern travel corridors to neighboring Texas and Mexico and north to Wichita and Kansas City.