Putnam County is situated in the lower Hudson Valley in the southeastern part of New York, between the Hudson River on its west and the New York-Connecticut border on its east. Depending on precise location within the county, road travel distance to New York City ranges between 45 miles (72 km) and 65 miles (105 km).
The terrain of the county is generally hilly. The region of the county nearest the Hudson River is especially so, and is part of the Hudson Highlands. The highest point in Putnam County is Scofield Ridge, with four summits at approximately 1,540 feet (469 m) above sea level. The lowest point is sea level along the Hudson. Between the hills and glacial moraine, Putnam County’s valleys contain numerous wetlands (including part of the Great Swamp), creeks, ponds, lakes (including the 583 acre Lake Mahopac), and reservoirs.