There are 86 US Post Offices in Harris County serving a total of 2,658,894 residents equating to 30,917 residents per post office. It's estimated that approximately 4,243,892 packages are handled across the 86 county post offices annually. 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. Harris County is included in the Houston\u2013The Woodlands\u2013Sugar Land Metropolitan Statistical Area."