Rockland is a city in and the county seat of Knox County, Maine, United States. As of the 2020 census, the town population was 6,936. The ci…Rockland is a city in and the county seat of Knox County, Maine, United States. As of the 2020 census, the town population was 6,936. The city is a popular tourist destination. It is a departure point for the Maine State Ferry Service to the islands of Penobscot Bay: Vinalhaven, North Haven and Matinicus.