State Route 26 (abbreviated SR 26) is part of Maine's system of numbered state highways. It is a major regional route running for 96.7 miles (155.6 km) from downtown Portland to the New Hampshire border near Upton, where it continues as New Hampshire Route 26. It is a multi-state route along with NH 26 and its short extension into Vermont.
The multi-state highway was first designated in 1922 as part of the New England road marking system as NEI 26. When the system was supplanted by the United States Numbered Highways in 1926, it was redesignated as state highways retaining the original number.
SR 26 begins in Portland. State route logs show its southern terminus at the intersection of Cumberland Avenue and Washington Avenue in the western end of the city center. It heads north on Washington Avenue. In the field, the southern terminus is signed at the intersection of Congress Street, Washington Avenue, and Mountfort Street in the eastern end of the city center, one block south of the Cumberland Avenue intersection with Washington Avenue. From here, SR 26 follows Washington Avenue northward and joins with I-295 / US 1 over Tukey's Bridge, splitting off immediately on the other side of the bridge to continue northwest on Washington Avenue. 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.
In Gray Village, SR 26 and SR 100 intersect with US 202, SR 4 and SR 115 with SR 100 splitting off. The Turnpike begins to turn northeast at Gray, as does SR 100, but SR 26 continues north and then northwest. SR 26 continues north through New Gloucester and Poland, where it intersects SR 11 before passing the Poland Spring Resort. SR 26 continues through western Mechanic Falls, Oxford (where it briefly shares pavement with SR 121), eastern Norway and Paris (where it shares pavement with SR 117). SR 26 starts to turn northwest as it continues through West Paris and Woodstock en route to Bethel, where it has an interchange with US 2 and SR 5 located near the northern terminus of SR 35. At this interchange, SR 26 turns northward along US 2 and SR 5, forming a three-route concurrency spanning 6 miles (9 km). Immediately after crossing into the town of Newry, SR 26 splits off to the northwest. The highway's northern reaches are in an isolated, mountainous region of the state. After leaving Newry, the highway passes through Grafton Notch State Park, located in the unorganized territory of North Oxford. SR 26 continues through the town of Upton before crossing into Cambridge, New Hampshire, where the highway continues as NH 26 westbound.
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. The existing roadway ran northward from Gray, hugging the Sabbathday Lake and then passed directly through the Shaker Village en route to New Gloucester, along current Shaker Road and Sabbathday Road. This, along with a second attempt in 1989, was rejected due to disagreement among the public and town officials of how the plan ought to be executed.