Harris County is a county located in the U.S. state of Texas; as of the 2020 census, the population was 4,731,145, 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, who founded the town of Harrisburg on Buffalo Bayou in 1826.