NY 112 begins at an intersection with County Route 80 in the village of Patchogue. The route proceeds northward as a four-lane commercial street as Medford Avenue. Near the intersection with Lakewood Street, NY 112 leaves the village of Patchogue, entering the town of Brookhaven. The route does not change going north, passing Medford Elementary School before entering interchange 53 of the Sunrise Highway in the census-designated place of North Patchogue. NY 112 crosses over the Sunrise, continuing north as Medford Avenue as the four-lane boulevard it was prior to the interchange. At the intersection with Shaber Road, the route bends to the northeast, changing names to Medford Road and crossing an intersection with CR 99, a four-lane arterial through Brookhaven. Continuing north from CR 99, NY 112 condenses down to two lanes, remaining a commercial arterial. NY 112 passes Tremont Elementary School before crossing Greenport Road, continuing northward into the census-designated place of Medford. In Medford, NY 112 continues north, crossing under the Long Island Rail Road's Greenport Branch next to the Medford station. After crossing under the tracks, NY 112 continues northeast through Medford, entering interchange 64 of the Long Island Expressway and expanding to four lanes once again before an intersection with CR 16. The route returns to two lanes after CR 16, passing east of Blue Ridge Golf Club and Holy Sepulchre Cemetery. At this point, NY 112 changes names from Medford Avenue to Port Jefferson–Patchogue Road. Continuing north through Brookhaven, NY 112 intersects a former alignment of itself, entering the census-designated place of Coram. In Coram, NY 112 bends to the northwest at an intersection with Grand Smith Road, immediately intersecting with NY 25. The two roads parallel each other westward, NY 112 becoming a residential street in the middle of a large housing complex in Coram before turning northward and into an at-grade interchange with CR 83. NY 112 continues north out of the interchange and Coram, turning northwest as a two-lane residential arterial. After Birchwood Road, NY 112 becomes commercial once again, bending further to the northwest. After the bend, NY 112 continues through Brookhaven, crossing a large shopping plaza into the census-designated place of Port Jefferson Station. In Port Jefferson Station, NY 112 intersects with NY 347, a wide arterial boulevard in the town of Brookhaven. The route continues northwest away from NY 347 as a four-lane commercial street, now under the moniker of Patchogue Road. Just after entering the downtown portion of Port Jefferson Station, NY 112 intersects with NY 25A. At this intersection, NY 112 terminates, the right-of-way continues north as NY 25A and Main Street, connecting to the namesake train station on the Port Jefferson Branch.
History
NY 112 was known as the Patchogue Stage Road in the 19th and early 20th centuries, serving as the main thoroughfare for New England residents taking stagecoaches from Port Jefferson to Patchogue. Additionally, the Medford Avenue segment in Patchogue and North Patchogue was part of the historic Long Island Bicycle Path, which ran from Patchogue to Port Jefferson in the 1890s and into the early 20th century. Most of the old stage road was acquired by the state of New York in 1913; however, the section within the Patchogue village limits did not become state-maintained until the 1920s. The Patchogue–Port Jefferson state highway did not receive a posted designation until the 1930 renumbering of state highways in New York, when it became NY 112. Parts of NY 112 have been realigned to bypass curves or turns in the original stage road. One former segment lies behind a New York State Department of Transportation maintenance yard in Coram. Other highways that were once part of NY 112 include part of Middle Island Road and an abandoned road in Medford; a section near Pine Road in Coram; and a segment near East Gate in Terryville. In the 1960s and 1970s, NYSDOT wanted to realign both NY 112 and NY 25 in Coram. Plans to realign NY 112 in this area date as far back as the 1930s. The route originally crossed the Long Island Rail Road in Medford by way of a dangerous grade crossing. It was replaced with a steel bridge in 1940, 13 years after a driver was killed while traversing the crossing. The bridge has a low clearance. In 1964, the segment of NY 112 in Patchogue between East Main and Clark streets was widened to four lanes. When the Long Island Expressway was built across central Suffolk County between 1969 and 1971, NY 112 was widened to a four-lane divided highway in the vicinity of the new expressway. This project included tilting the curved embankment of the southbound lane, which has created a series of floods in moderate to heavy rainstorms.
