Babylon to Montauk

From the junction between the non-electrified Central  Branch from Bethpage, on the north side and the third-rail electrified Montauk Branch from Jamaica via St. Albans, trailing in on the south side, and passenger station at Babylon (MP 36.8/36.6), end of electrified service from New York, the Montaul Branch heads just north of due east, third-rail electrified only as far as the yard on the south side, east of Babylon station, and non-electrified thereafter, past the passenger station at Bay Shore (MP 40.7), turning east, past the passenger station at Islip (MP 43.1), east-northeast past the passenger station at Great River (MP 45.2) and the bridge over the eponymous inlet, east-southeast past the passenger station at Oakdale (MP 47.4), and east-northeast, past the passenger station at Sayville (MP 49.8), the Block Limit Station at Y (MP 50.0), Bayport, Blue Point, and the passenger station at Patchogue and Block Limit Station at PD (MP 53.9), where the line reduces to single track with Block Limit Stations and sidings.

The line turns just north of due east, past the 28-car siding and passenger station at Bellport, and Block Limit Station at BO (MP 57.8), east-northeast past Brookhaven, just north of due east, past the passenger station at Mastic Shirley (MP 62.3) and the 26-car Controlled Siding from MS 1 (MP 62.4) to MP 2 (MP 62.7), just south of due east, past the 42-car siding and passenger station at Center Moriches, and Block Limit Station at MO (MP 66.3), north-northeast and then east-southeast, where an erstwhile line from Manorville trails in on the north side, past Eastport, the 30-car siding and Block Limit Station at PT (MP 69.0), and the passenger station at Speonk and Block Limit Station at SK (MP 71.6), just north of due east, past the 24-car siding and passenger station at Westhampton, and Block Limit Station at WH (MP 74.3) and the passenger station at Quogue (MP 77.0), where it turns east-northeast.

There is a 54-car siding and passenger station at Hampton Bays, and Block LImit Station at ND (MP 81.2), a bridge over a canal, a turn east-southeast, past Shinnecock Hills, the passenger station at Southampton Campus–LIU (MP 85.8), and the 43-car siding and passenger station at Southampton, and Block Limit Station at SN (MP 89.3), a turn northeast and then east-northeast, past Watermill, just north of due east, past the 22-car siding and passenger station at Bridgehampton, and Block Limit Station at BH (MP 94.0), where an erstwhile spur to Sag Harbor once headed north-northeast, Wainscott, the passenger station at East Hampton (MP 100.9), the 29-car siding and passenger station at Amagansett, and Block Limit Station at AG (MP 104.3), Promised Land, Fanny Bartlett and Napeague Beach, turning northeast, to the Block Limit Station at MY (MP 114.8), curving south and then east, to the passenger station at Montauk (MP 115.6), end of the line.