The Calhoun Mansion is the largest private residence in all of Charleston and may be seen on your carriage tour of this beautiful, historic city. Built in 1876 by George W. Williams, the mansion was his contribution to the reemergence of Charleston after the civil war.

The title of the biggest mansion in South Carolina historically belongs to Millford Plantation in Pinewood, but in terms of modern residential square footage in 2026, many point to the massive private estates on Kiawah Island and Hilton Head. Specifically, the Osprey Point Estate on Kiawah Island is often cited for its sheer scale, featuring over 15,000 square feet of living space. However, if looking at historical "great houses," the Nathaniel Russell House and the Williams Mansion (formerly Calhoun Mansion) in Charleston are the largest in terms of preserved urban grandeur, with the Williams Mansion boasting over 24,000 square feet, 30 rooms, and a 75-foot domed ceiling. In 2026, luxury real estate data shows a trend of "mega-mansions" being built in the Upstate region near Lake Keowee, some of which rival these historical figures in internal volume, though the historical mansions of the Lowcountry remain the most culturally significant "biggest" homes in the state.