Continuing north, SR 102 enters the town of Mount Desert and Acadia National Park.

Just before reaching Thompson Island in on the Trenton town line, the highway meets up with SR 3 once again.

It connects to SR 102 in Tremont and Southwest Harbor, passing through the Manset and Seawall areas along the way and running for 6.8 miles (10.9 km).

It forms a nearly complete loop and, for the most part, lacks cardinal directions on guide signs.

One exception is present in Tremont, where the first guide sign after departing from SR 102 indicates SR 102A south, although from this point the route also turns east, north, and west en route to Southwest Harbor.