Why the answer isn't obvious
Lowcountry municipal boundaries interleave: a James Island address may fall under the City of Charleston or unincorporated Charleston County; parts of Summerville reach into three counties; Daniel Island sits within the City of Charleston though it feels like its own town.
The permitting jurisdiction follows the legal boundary, not the neighborhood name — which matters because procedures and fees differ.
The main players
City of Charleston covers the peninsula, much of West Ashley, Daniel Island, and annexed portions of James and Johns Islands. Charleston County handles unincorporated areas including much of the rural sea-island territory.
Mount Pleasant, North Charleston, and Summerville run their own building departments, while Berkeley and Dorchester counties cover their unincorporated areas — including different slices of greater Summerville and Goose Creek's surroundings.
What this means for your project
For homeowners, the practical answer is simple: your licensed contractor determines the jurisdiction and pulls the permit there — that is part of the service. Where it matters to you is verifying that it happened, which any permit's paperwork shows.
When comparing bids, a contractor vague about which jurisdiction covers your address is waving a small flag worth noticing.
Historic districts add a layer
Downtown, exterior equipment placement can also involve preservation review on top of the mechanical permit — one more reason compact and quiet equipment choices matter on the peninsula.
We design placements with both inspectors and neighbors in mind; it is home-field knowledge.
