It is a major interregional route which runs nearly the entire length of the state from south to north.

The highway travels through York, Cumberland, Androscoggin, Kennebec, Somerset, Waldo, Penobscot, Piscataquis and Aroostook counties.

At 400.93 miles (645.23 km) in length, SR 11 is the longest state highway in Maine by a wide margin.

However, it is not the longest numbered route in Maine, as US 1 runs for over 526 miles (847 km) in the state.

SR 11, together with NH 11 and Vermont Route 11, forms a continuous multi-state route across northern New England that stretches for over 550 miles (890 km) from Manchester, Vermont to Fort Kent, Maine.

The number 11 dates back to 1922 when the New England road marking system was adopted, although Maine did not take part until 1925.

In 1931, the Maine State Highway Commission conducted an experiment in which it designated a new low-numbered state highway (SR 4) which ran mostly on existing alignments of the original 1925 intrastate routes (which were all numbered 100 and higher to avoid conflicts with the New England Interstate routes) and replaced several of the original numbers along those alignments.

By the time the renumbering project was finished, SR 11 was extended to 400 miles (640 km).

The original routing of SR 11 from the New Hampshire state line to downtown Sanford was maintained (and was overlapped by the newly designated US 202 in 1936).

The highway then used new routing between Waterville and Corinth, part of which was shared with the newly designated SR 43.

Although they share a route number, they are located over 180 miles (290 km) apart on SR 11.The southern segment of SR 11A is located in York County, entirely within the city of Sanford, and is 3.27 miles (5.26 km) in length.

Most of the route travels from north to south along one-way Penobscot Avenue through the central business district of the town.