Most of the island is tidal marsh, though approximately 800 acres (3.2 km2) of upland acreage exists on the northeastern portions.

The residential portion of the island was listed as a census-designated place in the 2020 census, with a population of 209.

[6] In November 2018, the South Carolina Environmental Law Project filed a lawsuit on behalf of the Harbor Island Owners Association, asking the Beaufort County Circuit Court to order the state to remove seven houses that, through rapid erosion, had ended up in the water on the beach below the mean high water mark.

[7] The state was released from the action in 2018, leaving the homeowners and the association as parties to the suit.

[11] Harbor Island has a Sea Turtle Nest Protection Program permitted by the South Carolina Department of Natural Resources and run by volunteers.