The river's headwaters are at Byram Lake in Westchester County, New York, at an elevation of , and flow southward, crossing the New York-Connecticut border and eventually flowing into Long Island Sound at Port Chester Harbor.
The river's source is situated at Byram Lake in Westchester County, New York, at an elevation of , and subsequently flows southward, crossing the border between New York and Connecticut before emptying into Long Island Sound at Port Chester Harbor.