Route 110, is a southwest–northeast state highway in Massachusetts. The route travels from West Boylston in Central Massachusetts to Salisbury near the coast. Route 110 is paralleled by Interstate 495 for most of its length, and interchanges with the freeway several times along its journey.
Route 110 begins at Route 12 in West Boylston, just north of the Wachusett Reservoir and the border with Worcester. The route follows north of the reservoir, passing through Sterling before entering Clinton. In Clinton, Route 110 shares a quarter-mile concurrency with Route 62 and Route 70 before heading northward, crossing the Nashua River and passing through Lancaster.
The route continues into Bolton, crossing Route 117 and passing the Bolton Flats before entering the town of Harvard. Route 110 continues through the village of Still River, wrapping around Bare Hill Pond before joining Route 111, starting a 3.7-mile long concurrency which crosses Route 2 at Exit 38, just east of Fort Devens. The concurrency with Route 111 ends in Ayer in Middlesex County at a rotary junction with Route 2A, where Route 110 begins a concurrency with Route 2A eastward into Littleton.
In Littleton, Routes 110 and 2A cross the Fitchburg Line railroad tracks before meeting I-495 at Exit 30, beginning Route 110's long relationship with the interstate. At Route 119. Route 2A leaves Route 110 to head eastward, with Route 110 entering Westford. In Westford, Route 110 shares a short concurrency with Route 225 before continuing just south of I-495, accessing the highway again off of Boston Road. Route 110 enters Chelmsford, meeting Massachusetts Route 4 and the western end of Route 129 at the center of town, just north of the northern end of Route 27. Route 110 then crosses I-495 at Exit 34, and then shortly meets U.S. Route 3 at Exit 31, just as Route 110 enters the city of Lowell.
In Lowell, Route 110 joins Route 3A near the Gallagher Transit Center and just north of the northern end of the Lowell Connector. Route 110 continues eastward, meeting the western end of Route 133 at Route 38, joining Route 38 to head northward across the Merrimack River via the Hunts Falls Bridge. Just north of the bridge the two routes split at a rotary, with Route 38 heading west and Route 110 heading east, following the northern bank of the Merrimack on a two-lane road through Dracut and into Methuen. Up until approximately 1997, the Methuen section was a four-lane road; its total length as a four-lane road was the same as the modern two-lane road is. The change to being a two-lane road thus was most likely due to safety.