In Maine, the IAT/SIA starts on the Katahdin Loop in the Katahdin Woods & Waters National Monument east of Baxter State Park. The trail generally follows the East Branch of the Penobscot River north through the Monument, before turning east towards Mount Chase and, eventually, Houlton. Just before Houlton, the trail turns north again and continues to and across Mars Hill Mountain in Aroostook County. It then follows the United States/Canadian international border northward to Fort Fairfield where it crosses into Perth-Andover, New Brunswick.
Length: 222km / 138mi.
Note: Length may vary depending on which spur trails or alternate routes are followed.