Saint Croix Island International Historic Site is best reached by private vehicle.  The site is located eight miles south of Calais, Maine, on U.S. Route 1, and can be reached either by Route 9 from Bangor or U.S. Route 1, the coastal route from Portland and points south. The parking lot is located on the left after entering the mainland site.

Several different airlines service airports at Bangor, Maine (103 miles), or Saint John, New Brunswick, Canada (80 miles). Car rentals are available at both airports.

The only visitor access to the island is by privately owned boats. Visits to the island are not encouraged due to its fragile nature.