Ranked by surface area computed from USGS National Hydrography Dataset (NHD) lake polygons — consistent federal geometry, not state-documented acreage; figures can differ modestly from traditionally cited ones.
The Great Lakes and Lake Champlain are excluded — Champlain spans New York, Vermont, and Québec, so its full surface would overstate a New York ranking.
Lakes whose mapped polygon could not be confidently matched are excluded rather than guessed.
Lakes under 50 acres are excluded from rankings.
Public access inventories are not yet tracked for New York here, so access is never shown or ranked.
FAQ
Cortland County lake records
What is the biggest lake in Cortland County?
Tully Lake — Tully Lake in Cortland County is the biggest lake within Cortland County by USGS NHD surface area, at 262 acres (Lake Champlain, shared with Vermont and Québec, is excluded).
Source data: USGS National Hydrography Dataset lake polygons as aggregated by LakeList. NHD-computed area can differ modestly from traditionally cited acreages.Lake outlines are shoreline shapes from LakeList and the USGS National Hydrography Dataset; they illustrate a lake's form and are not depth or navigation charts.