There are 12 US Post Offices in Jefferson County serving a total of 171,847 residents equating to 14,321 residents per post office. It's estimated that approximately 274,287 packages are handled across the 12 county post offices annually. Jefferson County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 252,273. The county seat of Jefferson County is Beaumont. The county was established in 1835 as a municipality of Mexico and was organized as a county in 1837. It is named for U.S. president Thomas Jefferson. Jefferson County is part of the Beaumont\u2013Port Arthur, TX Metropolitan Statistical Area and has the highest population of the four county MSA. It is located in Southeast Texas."