The sourthern end of NY 231 is the only constructed section of the Babylon-Northport Expressway, which was intended to run from NY 27A to NY 25A at the intersection with Elwood Road (CR 10). In 1982, the expressway was cancelled due to resident opposition.
| Mile | Northbound | Southbound | Notes |
|---|---|---|---|
| Suffolk County | |||
| Speed Limit 55 | |||
| 0.0 |  |
 Babylon Bay Shore |
At-grade intersection |
| 0.5 | John Street West Islip Babylon |
 |
|
| 1.5 |  EastMontauk |
||
| 1.5 | West New York |
||
| 2.2 | Hunter Avenue Freeway Ends |
 |
|
| Speed Limit 55 | |||
| Suffolk County | |||