It was renumbered to New York State Route 3B c. 1932 and extended northeastward to Knowlesville via Millville by 1932 before becoming NY 31A c. 1935.

The route was truncated to its current eastern terminus in the early 1980s after NY 31 was altered to bypass Brockport to the southwest.

NY 31A begins at a four-way intersection in the southern portion of the village of Medina.

It leaves the village shortly afterward, entering a rural area of Orleans County dominated by open fields.

[5] Past Millville, NY 31A becomes West Lee Road and heads southeastward through farmland to the Barre town line, at which point the route turns back to the east and follows a slightly northeasterly alignment for 5 miles (8 km) into the town of Albion.

Here, NY 31A passes the Benjamin Franklin Gates House, situated on the north side of the route near a junction with Mix Road.

NY 31A, now East Lee Road, continues on a northeasterly line for another 2.5 miles (4.0 km) before curving southward for 1 mile (1.6 km) to avoid a marshy area near the eastern town line.

[4] The highway retains an east–west alignment for 2 miles (3.2 km) to the outskirts of the hamlet of Clarendon, the largest community on the route since Medina.

Here, the amount of development along the route begins to increase, a change ushered in by a pair of large housing tracts in the eastern part of the community.