There are 5 US Post Offices in Lavaca County serving a total of 23,452 residents equating to 4,690 residents per post office. It's estimated that approximately 37,432 packages are handled across the 5 county post offices annually. Lavaca County (/l\u0259v\u02c8\u0251\u02d0k\u0259/) is a county located in the U.S. state of Texas. As of the 2010 census, its population was 19,263. Its county seat is Hallettsville. The county was created in 1846. It is named for the Lavaca River which curves its way South East through Moulton and Hallettsville before reaching the coast at Matagorda Bay."