The river, the valley, and the road all turn back to the east in the adjacent town of Carrollton, where US 219 Business leaves NY 417 to continue south toward I-86 exit 23 and on to Limestone and Bradford, Pennsylvania.

NY 417 continues to follow the Allegheny River and the nearby Southern Tier Expressway (STE) to the hamlet of Vandalia, the easternmost point of the reservation.

In Olean, NY 417 initially follows State Street across a heavily commercialized area before entering a more residential portion of the city.

East of here, NY 417 diverges from the STE as it crosses over Olean Creek and follows the Allegheny River into the slightly less populated town of Portville.

The first 2 miles (3.2 km) of NY 417 in Allegany County traverses isolated, undeveloped areas as it runs along the base of a large valley surrounding Oswayo Creek, a tributary of the Allegheny River.

[citation needed] NY 417, meanwhile, leaves Bolivar to the east, winding its way northeastward across the mountains of the Southern Tier to its next large community, the village of Wellsville.

The highway and the overlap both end just southeast of downtown Wellsville, at which point NY 417 continues northeastward through the residential eastern section of the village on Andover Road.

[citation needed] About 2 miles (3.2 km) from the village center, the development along NY 417 ceases as the route progresses generally northeastward through the narrow valley of Dyke Creek, closely paralleling the main line of the Western New York and Pennsylvania Railroad (WNYP).

[citation needed] Beyond Jasper, the road meanders through a valley surrounding Tuscarora Creek, heading generally eastward to a larger gully containing the Canisteo River and the village of Addison.

At this point, the railroad and NY 417 turn northeast to follow I-99/US 15 and the Tioga River into the hamlet of Gang Mills, a western suburb of Corning.

The route continues past Robert Dann Drive on South Hamilton Street, crossing over the Cohocton River and reconnecting to the Southern Tier Expressway at exit 44, a complex semi-directional T interchange that also connects I-86 and NY 17 to I-99 and US 15.

From here, the route proceeds into the village of Painted Post as North Hamilton Street, serving two blocks of mostly commercial properties before terminating at an intersection with NY 415.

[13][14] NY 17 was realigned in the 1930 renumbering of state highways in New York to follow more southerly alignments from Olean to Wellsville (via Ceres) and from Andover to Jasper (via Greenwood).

Ostensibly, this was due to the potential for the Allegheny Reservoir to flood and inundate part of the roadway; the closure may have also partially been invoked to discourage tourists from browsing the newly built Seneca resettlement area (Jimerson Town) that had been constructed around the road.

This stretch was abandoned in 1980 and left unattended by both the state and local governments, leading to the rapid deterioration of the roadway, including a bridge running over the reservoir (constructed in 1930) that remains standing but has since become a hazard.

[1] The Seneca Nation Allegany reservation governmental headquarters, along with the surrounding hamlet of Jimerson Town, lies on the eastern half of NY 951T.

[citation needed] The Seneca Nation and the state of New York began talks in March 2010 to rebuild the former NY 417 between Steamburg and Jimerson Town.