There are three main settlements on the island - Higher Town, Middle Town and Lower Town - in addition to a number of scattered farms and cottages, with a total population (2001 census) of 142.
The island had a hotel, St Martin's On The Isle, which closed in 2013, and one pub, The Seven Stones, in Lower Town, which is currently closed and for sale. Polreath guesthouse and tearoom is located in Higher Town, and one campsite, between Lower Town and Middle Town is also present. There are quays at Higher Town (the Higher Town Quay, used at high tide) and at Lower Town (the Hotel Quay, used at low tide). A bakery, St. Martins Bakery, is located at Higher Town.
At the northeast corner of the island is a large red-and-white daymark. It was erected in 1683 by Thomas Ekins, first steward of the Godophin Family to live on the islands.
It is a rendered granite circular tower 4.8 metres (16 ft) in diameter and 6.4 metres (21 ft) high, set back to conical termination making it 11 metres (36 ft) high. The blocked arched entrance door contains an incorrect date of 1637. It was painted white until 1822 but by 1833 had been painted red, and is now painted in bands of red and white.