There are 7 US Post Offices in Grimes County serving a total of 28,735 residents equating to 4,105 residents per post office. It's estimated that approximately 45,864 packages are handled across the 7 county post offices annually. Grimes County is a county located in the U.S. state of Texas. As of the 2010 census, its population was 26,604. The seat of the county is Anderson. The county was formed from Montgomery County in 1846. It is named for Jesse Grimes, a signer of the Texas Declaration of Independence and early settler of the county.