The Montauk Branch is a rail line owned and operated by the Long Island Rail Road in the U.S. state of New York. The line runs the length of Long Island, 115 miles (185 km) from Long Island City to Montauk. However, in LIRR maps and schedules for public use, the term Montauk Branch refers to the line east of Babylon; service from Jamaica to Babylon is covered by separate Babylon Branch schedules, while the line west of Jamaica is currently unused for passenger service. A select number of Montauk Branch trains operate via the Main Line and Central Branch during peak hours.

The westernmost portion of the Montauk Branch in Queens, known as the "Lower Montauk," runs between the Long Island City and Jamaica stations, mostly at street level with grade crossings. East of the Long Island City station, the abandoned Montauk Cutoff merges with the branch, after both cross Dutch Kills. The Lower Montauk Branch had nine stations, four of which were closed by 1940. The remaining five stations (Richmond Hill, Glendale, Fresh Pond, Haberman, and Penny Bridge) were closed on March 13, 1998, due to low ridership and incompatibility with then-new C3 bi-level coach cars that can only use high platforms (only Richmond Hill had an actual platform; the other four stations' platforms were just pavement strips beside the tracks). After these stations closed, the LIRR continued to use the Lower Montauk to operate non-stop trains between Jamaica and Long Island City rather than divert them to the Main Line; there were only two such trains at the time of the 1998 station closures, one westbound in the morning, and one eastbound in the evening. These two trains were re-routed north to Hunterspoint Avenue in 2012, effectively ceasing passenger train service on the Lower Montauk. Soon after, full control of the Lower Montauk was transferred to the New York and Atlantic Railway for freight operations.

The New York City Department of Transportation has periodically floated proposals to repurpose the Lower Montauk Branch for rapid transit operations. In 1984, the Department studied an option to connect the branch to the New York City Subway through a proposed connection to the IND 63rd Street Line in Long Island City. This proposal was unpopular in the communities surrounding the branch. In 2017, the Department studied a plan to operate light rail service on the Lower Montauk Branch.

After Penn Station opened in 1910, the Lower Montauk became primarily a freight route, and when the present Jamaica station opened in 1913, the two Lower Montauk tracks continued past the south side of the station, south of Hall tower and the south Union Hall Street platform and on to Holban Yard. Those two tracks now carry trains to/from the Hillside Facility that has replaced Holban Yard; they can also carry nonstop Main Line trains past Jamaica station. East from Jamaica the Montauk Branch runs between the Main Line tracks (with two usually westward Main Line tracks north of it and two eastward tracks south of it) until just west of Hillside Facility. At 40°42′21″N 73°47′04″W / 40.70585°N 73.7845°W / 40.70585; -73.7845 the Montauk Branch rises to cross above the other tracks and turns southeast. At 40°40′01″N 73°44′49″W / 40.667°N 73.747°W / 40.667; -73.747 it swings parallel to the Atlantic Branch between its Laurelton and Rosedale stations. The Montauk Branch east of Jamaica is 0.7 mile longer than the Atlantic.

The portion between Jamaica and Babylon stations has been electrified since 1925, and electric trains to Babylon are often identified as a separate service, the Babylon Branch. It is grade-separated on embankments or elevated structures. From Babylon east to Montauk, diesel-electric or dual-mode electric/diesel-electric locomotives haul trains of passenger coaches.

The electrified portion of the Montauk Branch ends in the village of Babylon. Some of the diesel trains on the Montauk branch begin or end their runs at Babylon station, connecting with electric trains there. Other Montauk diesel trains operate into New York City, to Jamaica station; Hunterspoint Avenue or Long Island City stations in Long Island City; or Penn Station.

The Montauk Branch, along with the parallel Atlantic Branch, spawns three subsidiary branches: the West Hempstead Branch, Far Rockaway Branch, and Long Beach Branch.

The terminal stations in diesel territory, east of Babylon, are Patchogue, Speonk, Southampton, and Montauk; South Fork Commuter Connection shuttles may short-turn at Hampton Bays and Amagansett. The Montauk Branch is double-tracked from just east of Long Island City (where there is a short segment of single track) all the way through Babylon, becoming single track at Y Interlocking east of the Sayville station. Some Montauk Branch trains operate west to NYC via the diesel-only Central Branch, joining the Main Line east of Bethpage station. Only a few actually run via the Montauk Branch west of Babylon, under normal conditions on the Main Line.

The Montauk Line has heavy ridership and frequent service as far as Patchogue station and commuter service as far as Speonk station. In the summer, with travelers going out to The Hamptons, Fire Island and other beaches, additional service is operated to the far eastern terminal at Montauk, such as the Cannonball, a Friday afternoon train departing from Penn Station (originally Hunterspoint Avenue) and running non-stop to Westhampton station in Westhampton.

The Montauk Branch was home to the last tower in North America that regularly used "hooping" train operations: PD Tower, in Patchogue. "Hooping" is the transfer of instructions to the engineer and conductor by attaching the folded orders to the "hoop", a rod several feet long with a loop at the end that is passed from the ground to a moving train by catching the loop on one's arm. The last train to get hooped at PD was train 2730 on May 6, 2006.

Currently, the Montauk Branch intersects with the Bushwick Branch, Bay Ridge Branch, West Hempstead Branch, and Central Branch, as well as the Main Line at Long Island City and Jamaica and the Atlantic Branch at Jamaica and Valley Stream; the Far Rockaway Branch and Long Beach Branch are connected via the Atlantic Branch at Valley Stream. In the past, junctions existed with the Rockaway Beach Branch (a quarter mile east of Woodhaven Boulevard), Southern Hempstead Branch (Valley Stream to Hempstead), Manorville Branch (Eastport to Manorville on the Main Line), and Sag Harbor Branch (Bridgehampton to Sag Harbor). In early times, the Scoot ran frequently between Greenport on the North Fork, "around the horn" on the Manorville Branch, and east to Sag Harbor. In their day, both of those villages were very busy, bustling ports.

The South Side Railroad of Long Island built the line from Bushwick, Brooklyn to Patchogue in the 1860s, and completed the new line to Long Island City in 1870. With the reorganization of the South Side as the Southern Railroad of Long Island in 1874 and its lease by the LIRR in 1876, this line became the Southern Railroad Division, Southern Railroad of Long Island Division, or simply Southern Division. Effective Sunday, June 25, 1876, all Southern Division passenger trains were rerouted to use the LIRR main line from Berlin Junction (west of Jamaica) to Rockaway Junction, and the LIRR's Rockaway Branch to Springfield Junction, where it crossed the Southern. This change resulted in the closure of the Southern's Berlin, Beaver Street (Jamaica), Locust Avenue, and Springfield stations. The old line between Jamaica and Springfield, which became freight-only, was renamed the Old Southern Road. The Southern was reorganized as the Brooklyn and Montauk Railroad in 1879, and on March 14, 1880, the name was changed from the Southern Division to the Montauk Division. Thus the old South Side Railroad, except between Jamaica and Springfield Junction, was now the Montauk Division.

The LIRR opened the Sag Harbor Branch, including the present Montauk Branch from Eastport to Bridgehampton, on June 8, 1870. On July 27, 1881, after the South Side became part of the LIRR, its line – then the Montauk Division – was extended east to the Sag Harbor Branch at Eastport. The Sag Harbor Branch east of Eastport became part of the Montauk Division, and the old line from Manor (Manorville) to Eastport became the Manor Branch. An extension to Montauk, splitting off the old Sag Harbor Branch at Bridgehampton, opened to Amagansett on June 1, 1895 and to Montauk by September, and the line between Bridgehampton and Sag Harbor reverted to the old Sag Harbor Branch name.

Electrification of the Montauk Division from Jamaica to Babylon was completed on May 20, 1925, and normal operation began the next day. The Central Extension between Bethpage and Babylon was reopened for freight trains that had run via the Montauk Division.

The Montauk station was initially near the center of a sleepy fishing village at the north end of Fort Pond (where Austin Corbin built a pier in his unsuccessful effort to have trans-Atlantic ships dock there.) The Great Hurricane of 1938 devastated the terminus area and tore up sections of the roadbed. The population center then moved two miles (3 km) to the south, away from the station.

In 1953, amid bankruptcy, the LIRR sought to abandon the Montauk branch east of Patchogue and operate bus service in its place. It cited low, predominantly non-commuter ridership and proximity to the Main Line, and potential savings of $450,000 per year. The Town of East Hampton protested this proposed closure, highlighting the potential for increased vehicular traffic due to lack of alternative means of travel, and the line ultimately remained open.

1998 saw the closure of three lightly used stations: Center Moriches, Quogue, and Southampton College. Bellport was also due to be closed at the same time, but was kept open and upgraded following community opposition. Southampton College was temporarily reinstated for the 2004 and 2018 U.S. Open tournaments at the nearby Shinnecock Hills Golf Club, along with a steel walkway over Montauk Highway. At the conclusion of the tournament, the walkway was dismantled and the temporary platform was removed.

On April 16, 2019, New York State Assemblyman Fred Thiele announced that funding to design improvements on the Montauk Branch would likely be included in the 2019–2020 state budget. The funding would be used by the LIRR to design three passing sidings to be installed on the line in single-track territory between Speonk and Montauk. The installation of passing sidings would allow for increased service on the South Fork Commuter Connection. MTA President and CEO Pat Foye said that improvements to the Montauk Branch were identified in the LIRR's request for the MTA's Twenty-Year Needs Assessment.

West Hempstead Branch trains split off at VALLEY interlocking, just east of Valley Stream station. Babylon Branch trains terminate at Babylon, while Montauk Branch trains continue beyond. Many non-electric Montauk Branch trains that run express between Jamaica and Babylon run via the Main Line and Central Branch, with limited service to Mineola and Hicksville stations.

Zone	Location	Services			Station	Miles (km) from LICvia Lower Montauk	Opened	Closed	Connections and notes
		WH	BB	MT
1	Long Island City, Queens			●	Long Island City (rush hours only)	–	1854		Long Island Rail Road: Oyster Bay and Port Jefferson branches NYC Subway: 7 and <7>​ (at Vernon Boulevard – Jackson Avenue) MTA Bus: Q103 NYC Ferry East River Ferry † Served by five peak round trip trains, one of which is Montauk train
					Penny Bridge		1854	1998
					Laurel Hill		1890	1900
	Maspeth, Queens				Haberman		1892	1998
					Maspeth		1895	c. 1924
					Fresh Pond		1869	1998	Originally named Bushwick Junction
	Glendale, Queens				Glendale		1869	1998
					Ridgewood		1883	1924
	Richmond Hill, Queens				Richmond Hill		1868	1998	Originally named Clarenceville
					Shops		c. 1900	1913	Part of the Morris Park Facility
					Dunton		1869 1876	1876 1939	Originally named Van Wyck Avenue, then Berlin
3	Jamaica, Queens	●	●	●	Jamaica	9.0 (14.5)	1836		Long Island Rail Road: Atlantic, Far Rockaway, Hempstead, Long Beach, Oyster Bay, Port Jefferson, Ronkonkoma branches New York City Subway: E​, ​J, and ​Z (at Sutphin Boulevard–Archer Avenue–JFK Airport) New York City Bus: Q20A, Q20B, Q24, Q30, Q31, Q43, Q44 SBS, Q54, Q56 MTA Bus: Q6, Q8, Q9, Q25, Q34, Q40, Q41, Q60, Q65 Nassau Inter-County Express: n4 AirTrain JFK: Jamaica Station Route
					Union Hall Street		c. 1890	1976	Originally named New York Avenue
					Canal Street		1890	1899
					Hillside		1890	1966
	St. Albans, Queens	●			St. Albans	11.8 (19.0)	1898		New York City Bus: Q4 Originally named Locust Avenue
	Springfield Gardens, Queens				Springfield Gardens		1870s	1979	Originally named Springfield
4	Valley Stream				Valley Stream	16.1 (25.9)	1869		Platform on Atlantic Branch tracks, though switches allow trains on the Montauk Branch to stop as needed. Nassau Inter-County Express: n1, Elmont Flexi
	Lynbrook		●		Lynbrook	17.7 (28.5)	1867		Long Island Rail Road: Long Beach Branch Nassau Inter-County Express: n4, n25, n31, n31x, n32 Originally named Pearsall's Corners, then Pearsall's
7	Rockville Centre		●		Rockville Centre	19.3 (31.1)	1867		Nassau Inter-County Express: n15, n16, n31x, Mercy Medical Shuttle
	Baldwin		●		Baldwin	21.2 (34.1)	1867		Nassau Inter-County Express: n35 Originally named Baldwinsville, then Baldwins
	Freeport		●		Freeport	22.7 (36.5)	1867		Nassau Inter-County Express: n4, n19, n19x, n40/41, n43, n88x
	Merrick		●		Merrick	24.1 (38.8)	1867
	Bellmore		●		Bellmore	25.6 (41.2)	1869
	Wantagh		●		Wantagh	25.9 (41.7)	1867		Originally named Ridgewood
	Seaford		●		Seaford	27.7 (44.6)	1899		Nassau Inter-County Express: n54
	Massapequa		●		Massapequa	28.7 (46.2)	1867		Nassau Inter-County Express: n54, n55, n80 Originally named South Oyster Bay
	Massapequa Park		●		Massapequa Park	29.5 (47.5)	1933		Nassau Inter-County Express: n54, n55, n80
	East Massapequa				Unqua		1880	1881
9	Amityville		●		Amityville	30.6 (49.2)	1868		Nassau Inter-County Express: n54, n55, n71 Suffolk County Transit: 1, 2, 4, 10
	Copiague		●		Copiague	32.4 (52.1)	1902
					Belmont Junction		1875	1876
	Lindenhurst		●		Lindenhurst	33.7 (54.2)	1867		Suffolk County Transit: 10 Originally named Wellwood, then Breslau
	Babylon		●	●	Babylon	36.6 (58.9)	1867		Suffolk County Transit: 2, 3, 5, 10, 15 Originally named Seaside Terminus of electrification
10	Bay Shore			●	Bay Shore	40.7 (65.5)	1868		Suffolk County Transit: 2, 7, 11, 12 Originally named Penataquit, then Bayshore
	Islip
					Islip Centre		1868	1869
				●	Islip	43.1 (69.4)	1868
	East Islip
					Club House		1870	1897
				●	Great River	45.2 (72.7)	1897		Originally named Youngsport
	Oakdale			●	Oakdale	47.4 (76.3)	1868		Suffolk County Transit: 2
	Sayville			●	Sayville	49.8 (80.1)	1868		Sayville Ferry Service to Fire Island
	Bayport				Bayport		1869	1980
	Blue Point				Blue Point		1870 1900	1882 1980
	Patchogue			●	Patchogue	53.2 (85.6)	1869		Suffolk County Transit: 2, 6, 51, 53, 55, 66, 77, 77Y Patchogue Village Bus Davis Park Ferry to Fire Island
	East Patchogue				East Patchogue		1890	1928
	Hagerman				Hagerman		1890	1929
12	North Bellport			●	Bellport	57.8 (93.0)	1882		Suffolk County Transit: 66, 77 Originally named Accobomac, then Brewster Place
	Brookhaven				Brookhaven		1884	1958
	Shirley			●	Mastic–Shirley	62.3 (100.3)	1960		Suffolk County Transit: 66
	Mastic				Mastic		1882	1960	Originally named Forge
	Center Moriches				Center Moriches		1881	1998	Originally named Moriches
	East Moriches				East Moriches		1897	1958
	Eastport				Eastport		1870	1958	Originally named Moriches
	Speonk			●	Speonk	70.8 (113.9)	1870
14	Westhampton			●	Westhampton	74.3 (119.6)	1870
	Quogue				Quogue		1875	1998
	East Quogue				East Quogue		1871	c. 1883	Originally named Atlanticville
	Hampton Bays			●	Hampton Bays	81.2 (130.7)	1871		Suffolk County Transit: 92 Originally named Good Ground
					Canoe Place		1935	1953
					Suffolk Downs		1907	1921
	Shinnecock Hills				Shinnecock Hills		1887	1932
					Southampton College		1907 1976 1986	1939 1998 1986	Originally named Golf Grounds, then Southampton Campus Temporarily reopened for the 1986 U.S. Open, 2004, and 2018 U.S. Opens
	Southampton			●	Southampton	89.3 (143.7)	1871		Suffolk County Transit: 92, on-demand
	Water Mill				Water Mill		1875	c. 1968	Originally named Watermill
	Bridgehampton			●	Bridgehampton	94.0 (151.3)	1870
	Wainscott				Wainscott		1898	1938
	East Hampton			●	East Hampton	100.9 (162.4)	1895		Suffolk County Transit: 92, on-demand Originally named Easthampton
	Amagansett			●	Amagansett	104.3 (167.9)	1895		Suffolk County Transit: on-demand
	Napeague				Napeague Beach		1895	1927
					Fanny Bartlett		1924	1928
					Promised Land		c. 1900	1928
	Montauk			●	Montauk	115.8 (186.4)	1895		Suffolk County Transit: on-demand

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