Lavaca County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 20,337. Its county seat is Hallettsville. The county was created in 1846. It is named for the Lavaca River, which curves its way southeast through Moulton and Hallettsville before reaching the coast at Matagorda Bay.

Hallettsville is a city in Lavaca County, Texas, United States. Its population was 2,731 at the 2020 census. It is the county seat of Lavaca County. Hallettsville also has a sizable German-Texan population, as the town founders were mainly German and Czech immigrants.