Visitors to Fort Ontario State Historic Site today will see the star-shaped fort dating to the early 1840's with 1863 – 1873 improvements. The fort is currently open to the public, but is undergoing renovation to its two officer's quarters; one of which is furnished. There is a video of the rooms undergoing renovations as well as those parts of the fort which are difficult to access. Another video depicts how the officer's quarters and army offices appear when furnished.

Underground artillery casemates and rifle galleries, Powder Magazine, East and West Guardhouses, Storehouse, and ramparts, featuring magnificent views of Lake Ontario, are available for touring. The fourth and current Fort Ontario was built on the ruins of three earlier fortifications dating to the French and Indian War, Revolutionary War, and War of 1812; it was occupied by the U.S. Army through World War II.

From 1944 – 1946 Fort Ontario served as the only refugee camp in the United States for victims of the Nazi Holocaust under the special order of President Franklin D. Roosevelt. A post cemetery containing the graves of 77 officers, soldiers, women, and children who served at Fort Ontario in war and peace is situated on the grounds.

In 1946 Fort Ontario was transferred to the State of New York and housed World War II veterans and their families until 1953; it opened as a state historic site in 1949.