[4] Located in the glaciated Appalachian Plateau area of Central New York, midway between Syracuse and Binghamton, this predominantly rural county is the southeastern gateway to the Finger Lakes Region.

Scattered archaeological evidence indicates the Iroquois also known as the Haudenosaunee controlled the area beginning about AD 1500.

It became part of the Military Tract, when, in 1781, more than 1¼ million acres (5,100 km2) were set aside by the State's Legislature to compensate two regiments formed to protect the State's western section from the English and their Iroquois allies, at the close of the Revolution.

To encourage settlement in the upstate isolated wilderness, the State constructed a road from Oxford through Cortland County to Cayuga Lake in 1792–94.

In 1784, following the peace treaty that ended the American Revolutionary War, the name of the county was changed to honor General Richard Montgomery, who had captured several places in Canada and died attempting to capture the city of Quebec, thus replacing the name of the locally unpopular British governor.

Eastern New Yorkers and New Englanders, wanting new land to farm, welcomed the opening of this frontier.

The first white settlement in the county was made in 1791 by Amos Todd, Joseph Beebe and Rhoda Todd Beebe, emigrants from Connecticut who paddled up the Tioughnioga River from Windsor, to live near the head of navigation in the Town of Homer.

Thus, Cortland County was created from the southern half of Onondaga County as part of the Boston Ten Towns on April 8, 1808, and was named in honor of the Pierre Van Cortlandt family - Pierre, Sr. having been the first lieutenant governor of the state.

The 76th was in most of the major battles the Army of the Potomac fought from Second Bull Run through Petersburg, at which time the three-year enlistment of most of the men ran out and the 300 or so men remaining from the 1,100 who left Cortland either returned home or transferred to other units.

At the Battle of Gettysburg, the 76th New York was one of the first infantry regiments on the field, holding down the extreme right of the Union line on the first day.

Republican George W. Bush carried the county in 2000 and 2004, defeating Al Gore by less than 1% in 2000, and John Kerry by just over 4% in 2004.

[6] The last Democrat to win a majority in Cortland County prior to Obama was Lyndon Johnson in 1964.

In 2020, Cortland County's streak of voting for the winner ended, as Joe Biden defeated Republican incumbent Donald Trump.