Richland.

Richland County handles building permits for all unincorporated areas and several smaller municipalities that contract for services. The City of Columbia operates its own independent building and zoning department for properties within its city limits. Development in unincorporated areas is subject to specific flood hazard overlays and stormwater management requirements managed by the county.

How this fits with the state

The state authority here is South Carolina Contractor's Licensing Board; Residential Builders Commission. The county file does not replace that — it adds the permit office, local overlays, and the actual filing path.