Niagara County is a county located in the U.S. state of New York. As of the 2010 census, the population was 216,469. The county seat is Lockport. The county name is from the Iroquois word Onguiaahra; meaning the strait or thunder of waters.\
It is the location of Niagara Falls and Fort Niagara, and has many parks and lake shore recreation communities. In the Summer of 2008 Niagara County celebrated its 200th Birthday with the first town of the county, Town of Cambria.
When counties were established in the New York colony in 1683, the present Niagara County was part of Albany County. This was an enormous county, including the northern part of New York State as well as all of the present State of Vermont and, in theory, extending westward to the Pacific Ocean. This county was reduced in size on July 3, 1766 by the creation of Cumberland County, and further on March 16, 1770 by the creation of Gloucester County, both containing territory now in Vermont.
On March 12, 1772, what was left of Albany County was split into three parts, one remaining under the name Albany County. One of the other pieces, Tryon County, contained the western portion (and thus, since no western boundary was specified, theoretically still extended west to the Pacific). The eastern boundary of Tryon County was approximately five miles west of the present city of Schenectady, and the county included the western part of the Adirondack Mountains and the area west of the West Branch of the Delaware River. The area then designated as Tryon County now includes 37 counties of New York State. The county was named for William Tryon, colonial governor of New York.
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 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.
Niagara County was created from Genesee County in 1808. It was, however, larger than the present Niagara County even though it consisted of only the Town of Cambria.
In 1821, Erie County was created from Niagara County.
The county has a number of properties on the National Register of Historic Places.