Flight
Portland is about an hour and a half from Camden, and has more rental car options available at the airport.
Flight
Bangor is a little closer at about an hour away, but is a little smaller with fewer local rental car options.
Travel Note
You won't find traditional chain hotels local to Camden, with the exception of the Hampton Inn in Rockland. The area is home to many small inns, bed & breakfasts, and motels all of which are great options. Many of these are also close enough to walk into town so definitely check them out on the map before deciding! Alternatively there are a large number if airbnbs locally.