From there, it runs generally northwesterly through the towns of New Windsor, Newburgh, and Shawangunk, to a junction with NY 208 near the hamlet of Wallkill.

NY 300's two major changes of direction are marked by slightly unorthodox intersections with other state highways.

Following that, the highway begins to curve to the west ahead of an intersection with County Route 69 (CR 69), named Union Avenue.

The route follows the Thruway to the New Windsor–Newburgh town line, where NY 300 expands to two lanes in both directions as it crosses into Newburgh.

The next three miles (4.8 km) of NY 300 serves as the town's main commercial strip, featuring several national chain stores and smaller, more local businesses.

The hamlet is named for Silas Gardner, an early settler whose stone house is still in use just north of the intersection, past the Orange Lake outlet brook.

Now named Union Avenue Extension, NY 300 heads northeast, crossing Gardnertown Road at an intersection with a full four-way traffic light.

Beyond Chadwick Lake Park, this section of NY 300 is largely a rural two-lane road that serves as a connector between Newburgh and Wallkill, a hamlet in the adjacent Ulster County town of Shawangunk.

Motorists proceeding straight at this intersection had a direct route to the Newburgh waterfront and the Newburgh–Beacon Ferry across the Hudson River.

The large signs on Interstate 84 still refer to NY 300 as Union Avenue, however, even though local and official use of this name has been suppressed for the past decade.

[14] When the New York State Thruway opened near Newburgh in 1955, exit 17 was a standard trumpet interchange that connected to Union Avenue and NY 17K.

No direct connection was built between I-84 and the Thruway, forcing traffic to utilize a short stretch of Union Avenue.

The inadequate cloverleaf design of the junction between I-84 and Union Avenue led to problems, especially with articulateds, which must slow significantly to negotiate the sharp loop slips, and weave with traffic attempting to leave the freeway westbound.

For many years state and local officials had wanted to build a direct connection between I-84 and the Thruway; however, federal funding did not become available until the very end of the 20th century.

The junction between the Thruway and Interstate 84 works were begun in 2001 but the project was delayed when the original contractor for the job was found to have ties to organized crime.