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 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.
In 1789, the size of Montgomery County was reduced by the splitting off of Ontario County from Montgomery. The actual area split off from Montgomery County was much larger than the present county, also including the present Allegany, Cattaraugus, Chautauqua, Erie, Genesee, Livingston, Monroe, Niagara, Orleans, Steuben, Wyoming, Yates, and part of Schuyler and Wayne Counties.
In 1791, Herkimer County was one of three counties split off from Montgomery (the other two being Otsego, and Tioga County). This was much larger than the present county, however, and was reduced by a number of subsequent splits.
In 1794, Onondaga County was split off from Herkimer County. This county was larger than the current Onondaga County, including the present Cayuga, Cortland, and part of Oswego Counties.
In 1798, a portion of Herkimer County, together with a portion of Tioga County, was taken to form Chenango County. Another part of Herkimer was split off to form Oneida County. This county was larger than the current Oneida County, including the present Jefferson, Lewis, and part of Oswego Counties.
In 1802, parts of Herkimer and two other counties (Clinton and Montgomery Counties) were combined to form the new St. Lawrence County.
According to the U.S. Census Bureau, the county has a total area of 3,777 km˛ (1,458 mi˛). 3,655 km˛ (1,411 mi˛) of it is land and 122 km˛ (47 mi˛) of it is water. The total area is 3.23% water.
There are 25,734 households out of which 30.60% have children under the age of 18 living with them, 51.20% are married couples living together, 10.30% have a female householder with no husband present, and 33.50% are non-families. 27.60% of all households are made up of individuals and 13.70% have someone living alone who is 65 years of age or older. The average household size is 2.46 and the average family size is 2.99.
In the county the population is spread out with 24.40% under the age of 18, 8.30% from 18 to 24, 26.60% from 25 to 44, 24.00% from 45 to 64, and 16.80% who are 65 years of age or older. The median age is 39 years. For every 100 females there are 94.20 males. For every 100 females age 18 and over, there are 91.70 males.
The median income for a household in the county is $32,924, and the median income for a family is $40,570. Males have a median income of $29,908 versus $21,518 for females. The Per capita income for the county is $16,141. 12.50% of the population and 8.90% of families are below the Poverty line. Out of the total population, 15.60% of those under the age of 18 and 10.40% of those 65 and older are living below the poverty line.