The number 26 dates back to 1922 when the New England road marking system was adopted, although Maine did not officially join until 1925.

SR 100 joins at Allen Avenue, and the two routes turn north onto Auburn Street and continue together as far as the town of Gray.

En route, the highway passes through the town of Falmouth, paralleling Interstate 95 (the Maine Turnpike) for the entire 13-mile (21 km) stretch.

After leaving Newry, the highway passes through Grafton Notch State Park, located in the unorganized territory of North Oxford.

In 1988, the first attempt was made to modify the existing routing of a 5.25-mile (8.45 km) stretch of SR 26 in the towns of Gray and New Gloucester.

Plans were resurrected in 1996 with the formation of a Public Advisory Committee of thirteen members, composed of local citizens, local/regional government officials, and residents of the Shaker Village.

Other deficiencies were also addresses, such as hazards to pedestrians, truck noise and excessive vehicular traffic passing through the Village, and storm/lake water quality concerns.

Truck lanes were added on uphill climbs to improve traffic flow, and connecting roads from SR 26 provide access to the Sabbathday Lake area.

Upon passing west of the lake, SR 26 rejoins its old alignment along former Sabbathday Road, which now dead-ends at its north end.

With the bypass, Turnpike traffic to or from points north of Gray no longer has to pass through the village center.