Petersburg, the first seat of Lavaca County when the county was organized in August 1846, was located six miles southeast of Hallettsville on Farm Road 2616 and the east bank of the Lavaca River. Petersburg's first post office was granted in 1848; William T. Townsend was the postmaster. The townsite, 300 acres of land given by Arthur Sherill in 1846, was near Zumwalt Settlement, which Adam Zumwalt and his family had established in the early 1830s. Petersburg was on the San Felipe-Gonzales-San Antonio and the Victoria-Columbus roads. The population was twenty in 1848, when John Williams opened a store. Town lots did not sell rapidly, and it was not until the single building which was used as courthouse, church, school, and sheriff's office burned to the ground that a courthouse was constructed in mid-1850s. For a time county business was held in various buildings or under the trees, and prisoners were locked in barns and boarded in private homes. In a bitterly contested election in 1852 Hallettsville was made the county seat; it required most of the town's manpower and arms to secure the county archives from the irate citizens of Petersburg. The matter was not settled until a final legal decision in 1860. In the 1850s E. H. Nelson and his wife established Nelson Academy, using the courthouse and the old Spencer Townsend tavern to house the academy's boarders. During the Civil War the school had to close for lack of pupils. In 1876 the post office was moved to Williamsburg, where John Williams operated a large storehouse, gristmill, and gin. By 1880 Petersburg had only one establishment. The one building on the site in 1963 was a home which was built with the old post oak lumber from the Petersburg courthouse.