[3] The county name is from a Mohawk-language word meaning "the pouring out place", referring to the point at which the Oswego River feeds into Lake Ontario at the northern edge of the county in the city of Oswego.

Oswego County is part of the Syracuse, NY Metropolitan Statistical Area.

In the years prior to 1776, most of the Loyalists in Tryon County fled to Canada.

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

This was much larger than the present county, however, and was reduced by a number of subsequent splits.

At various times, beginning in 1847 and as late as 1975, attempts were made to move the county seat to the Village of Mexico.

On April 20, 2002, at around 6:50 am, many residents of Oswego County were shaken awake by a magnitude 5.2 earthquake centered near Plattsburgh, New York.

During February 1–12, 2007, a major lake effect snowfall dumped over 10 feet (3 m) of snow in many places in Oswego County, resulting in several roof collapses, some communities being cut off, and some people being snowed-in in their homes.

A state of emergency was declared for the county, and the National Guard was sent in to help clear the snow.

[4] Oswego County is in northwestern New York State, just north of Syracuse and northwest of Utica, on the eastern shore of Lake Ontario.

[5] The Salmon River Falls, a 110-foot (34 m) waterfall, is a popular sightseeing destination in the northeastern portion of the county.

15.5% were of Irish, 14.0% German, 13.7% Italian, 13.3% English, 9.6% American, 7.9% French and 5.3% Polish ancestry according to Census 2000.

Retail made up the next most prominent sector, totaling $1.2 billion or more than $10,000 per resident.

[19][20] The Oswego County Legislature has 25 members, elected from equal population districts, reduced from 36 in 1993.

The seven standing committees as of December 2019 were Government, Courts and Consumer Affairs; Public Safety; Infrastructure, Facilities and Technology; Economic Development and Planning; Health; Human Services; and Finance and Personnel.

[22] In the 2019 general election, the county GOP won three more seats previously occupied by Democrats, expanding its control of the legislature to 23–2.