The Main Line then continues east from Mineola to Hicksville, where the two track Port Jefferson Branch begins and curves to the north.

From FARM Interlocking (just east of Farmingdale station), the Main Line continues to Ronkonkoma, except for some freight sidings along the route.

[10] Laws passed on April 19, 1859 allowed for the appointment of commissioners, empowered to contract with the LIRR to close the Cobble Hill Tunnel, cease using steam within city limits, and instead run horse cars for freight and passengers to the city line or East New York, connecting with steam trains to and beyond Jamaica there.

[16]: 114, 115, 120 [18]: 87  Service resumed on May 30, 1883 with one daily train in each direction after the managers of the cemetery made a request to the directors of the Long Island Rail Road.

[29][30] The Cut-Off shortened the Main Line by 328 feet (100 m),[31] and sped up service with the construction of a new straightened four-track route that ran at a lower grade.

[30] On November 20, 1908, the New York Public Service Commission approved the LIRR's application to complete the Maple Grove Cut-Off.

[25]: 2  The project entailed building six electrified tracks between Woodside and the Winfield Junction station, four for the Main Line and two for the North Side Railroad (now Port Washington Branch), with seven steel viaducts carrying the LIRR diagonally over the intervening street grid.

At the time, the Main Line tracks were elevated at Jamaica, and then descended on a steep grade to the east of the station to a level 20 feet (6.1 m) lower.

The LIRR planned to replace existing stations at Hillside and Union Hall Streets with more up-to-date facilities with full length concrete high-level platforms.

The Oyster Bay Branch, which left the main line at Mineola, was partially electrified in June 1934 north to East Williston station.

The LIRR had said that it anticipated a loss of annual revenue between $750,000 and $1 million with the opening of the extension of the Independent Subway System's Queens Boulevard Line to Jamaica.

[66] On April 22, 1957, work began on a $12,500 project to extend the station platform at Hicksville by 470 feet to allow trains to stop without blocking grade crossings at Broadway and Jerusalem Avenue.

The LIRR had completed similar platform extension projects at Manhasset, Bethpage, Westbury, Copiague, Malverne, and Brentwood.

It authorized engineering studies for the extension of electrified service along the Main Line from Mineola to Hicksville, then along the Port Jefferson Branch to Huntington.

[48] In October 1979, work began on a $525,000 project to extend the platforms at New Hyde Park station to accommodate ten-car trains.

[78] On February 1, 1980, the LIRR, in response to audit released by the state comptroller on November 16, 1979, submitted a proposal to close 29 stations, including Kew Gardens, to save $250,000.

In addition to Kew Gardens, Forest Hills, East Hampton, Westhampton, Sea Cliff and Locust Valley would be completely closed.

[79] As part of the MTA's first capital program, the signaling system on the Main Line between Jamaica and Penn Station would be upgraded to reduce congestion and allow for increased capacity.

The project would construct a new control center at Penn Station, allowing for remote control of Harold Interlocking, redesign Harold Interlocking, modernize towers and switching systems at Penn Station, and install reverse-signaling on the Main Line, allowing for increased peak direction capacity without adding additional tracks.

[90] By the 1990s, there was also an increased number of reverse commuters on the LIRR, and further improvements to the Main Line were needed, including the extension of electrification from Ronkonkoma to Yaphank and the installation of a third track from Bellerose to Hicksville.

[91] On April 28, 1998, a bridge over Herricks Road opened, replacing a grade crossing which was once "labeled the most hazardous in the United States by the National Transportation Safety Board."

[92] On October 30, 2013, the LIRR unveiled a renovated Queens Village station, with passenger elevators, improved lighting, security cameras and a repainted building.

[93] In the Metropolitan Transportation Authority (MTA)'s 2010–2014 capital program, it proposed lengthening the four-car-long platforms at Kew Gardens to allow additional train cars to board at the station.

[96] On July 26, 2018, it was announced that the LIRR planned to extend the platforms at Kew Gardens and Forest Hills by 200 feet (61 m) to accommodate six-car trains.

[112] The expansion will use space already owned by the MTA located immediately to the south of the existing rail yard and north of MacArthur Airport.

The Deer Park option was dismissed as it would have impacted several grade crossings, duplicated employee facilities and as it would not have benefited riders east of the station.

This short segment would eventually become the eastern end of the Third Track, and already allowed for a slight increase in peak-hour service upon its completion.

[129][130][131][132] In January 2016, Governor Andrew Cuomo announced a transportation improvement plan which included several million dollars in funding to restart third track development.

"[137] In December 2017, the LIRR awarded a contract for the project to the consortium 3rd Track Constructors for $1.8 billion, with construction beginning in 2018 and completion estimated for 2022.

[147][148] The MTA built the Elmont-UBS Arena station in Elmont, New York, as part of the Belmont Park redevelopment in the early 2020s.