Harris County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 4,092,459, making it the most populous county in Texas and the third-most populous county in the United States. Its county seat is Houston, the largest city in Texas and fourth-largest city in the United States. The county was founded in 1836 and organized in 1837. It is named for John Richardson Harris, an early settler of the area.