Historically, the island made up a large part of the old Gimsøy Municipality which existed from 1856 until its dissolution in 1964.

In the north and west, the island is flat and marshy, with the exception of the 368-metre (1,207 ft) tall Hoven mountain.

There are large protected areas in Gimsøya related to fauna and bird life.

"Gimsøy marshes nature reserve" (Gimsøymyrene naturreservat) is located on the island.

The north-facing part of Gimsøy has great views of the open ocean, and is a popular place to watch the midnight sun.