Blacks House, Williams House, possibly or Williams Manor, is the largest house in South Park . It's seen in the Episodes Here Comes The Neighborhood & Christan Rock Hard. The Blacks, formerly the Williams, are able to afford it because they "have more lucrative jobs," being a lawyer & chemist, unlike the rest of the town who have low-paying jobs (such as Liane Cartman who makes a living as a crack whore).
Very little is known about the house due to how big it is, but it does have an original Van Gogh painting and many corridors.