The Hudson River basin mostly lies in east-central New York, with small portions extending into southwestern Vermont, western Massachusetts, and northern New Jersey. The Hudson River, which is located almost entirely within New York, flows about 315 mi from its source in the Adirondack Mountains to its mouth at New York Harbor. The lower 161 mi is an estuary.

The headwaters of one of the major tributaries of the Hudson River, the Hoosic River, and of two more minor tributaries, Kinderhook Creek and the Roeliff Jansen Kill (Bash Bish Brook), lie in western Massachusetts. The Hoosic River, which is about 65 mi long, is the longest of west-flowing tributaries of the Hudson River.