The route was gradually moved onto its current alignment between Cairo and Claverack in the 1950s and 1960s, and realigned on its western end in 1984 to serve Cortland County.

It heads east across the Otselic River and through the hamlet of Lower Cincinnatus before curving to the northeast and crossing into Chenango County very soon afterward.

Across the county line, it continues northeast through a lightly developed valley surrounding Brakel Creek to the Pharsalia State Wildlife Management Area, where it connects with CR 42,[citation needed] a highway that was once part of NY 23.

The route crosses the river just east of South New Berlin, putting it into the equally hilly and rural Otsego County.

[citation needed] In the adjacent Delaware County, NY 23 initially follows a generally easterly routing through the Charlotte Creek valley.

After Davenport, a hamlet 8 miles (13 km) east of Oneonta, the road begins to climb onto the Catskill Plateau.

By the time it intersects NY 10 at the village of Stamford,[citation needed] it has already reached an elevation of 1,820 feet (555 m) above sea level.

[8] Elevation drops slightly upon reaching the hamlet of Grand Gorge within the town of Roxbury, located just above a small pond alongside NY 30 that gives rise to the Delaware's East Branch.

Shortly past Red Falls, all crossings of the creek come to mark the Blue Line that delineates the Catskill Park.

The route remains to the north of the creek even as it passes the Windham Mountain ski area and NY 296 comes in from the south.

[12] From here, NY 23 begins a long descent down the Catskill Escarpment, losing most of the elevation it had gained since leaving Oneonta.

[13] As it does so, the route provides sweeping, panoramic views of the Capital District and points north, east and west.

[citation needed] Once across the bridge and into Columbia County, the highway encounters NY 9G near the Olana State Historic Site in western Greenport.

[15] NY 23 continues to the southeast, bypassing Hudson well to the south and serving Columbia–Greene Community College, located in an otherwise forested area of Greenport.

[citation needed] In the center of the hamlet, US 9 and NY 23 encounter a complex intersection that features a total of four routes.

It proceeds generally easterly across mostly undeveloped fields to Martindale, a small community at the interchange linking NY 23 to the Taconic State Parkway.

Almost 3 miles (5 km) to the east, NY 23 reaches the state line, where it becomes Massachusetts Route 23 as it serves the bi-state Catamount Ski Area.

Two stretches of the highway, one from Catskill to Cairo and one from a few miles east of Stamford to West Harpersville, were also once part of the Susquehannah Turnpike.

[16] The Susquehannah Turnpike aided the growth of Greene County, which until then had depended on steamboats on the Susquehanna River and Catskill Creek.

[18] From Cairo to Stamford, the Susquehanna took a more northerly alignment, while NY 23 follows the turnpike of the Schoharie Kill Bridge Company, chartered in 1801.

[32][33] Plans were made in the early 1950s to construct a southern bypass of the city of Hudson between the Rip Van Winkle Bridge and NY 23 midway between Claverack and Hollowville.

[34][35] Construction on the portion of the highway between the bridge and US 9 south of Hudson began in the mid-1950s[15][36] and was completed in the late 1950s as a realignment of NY 23.