What Borders Lake Ontario? Two Countries, Two Provinces, Two States

Lake Ontario—the easternmost and smallest-by-surface Great Lake—forms a natural international boundary with a unique political geography:

North (Canada)

• Ontario – North shore: Toronto, Hamilton, Kingston, Niagara-on-the-Lake.
• Quebec – Only at the extreme northeastern outlet (St. Lawrence River head), a tiny sliver near Cornwall.

South (United States)

• New York – Entire U.S. shoreline: Rochester, Oswego, Sackets Harbor, Thousand Islands region.
• Pennsylvania – Does NOT border Lake Ontario. (Common error. PA borders Lake Erie only.)

Key Features

• Outlet: St. Lawrence River (only Great Lake outlet to Atlantic).
• Islands: Wolfe Island (largest), Amherst Island, Thousand Islands archipelago.
• Depth: 244 m (802 ft) max—second deepest Great Lake.

Correction: Only Ontario, Quebec (minimally), and New York border Lake Ontario. Pennsylvania is on Lake Erie.