When counties were established in the
Province of New York in 1683, the present Jefferson 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 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 subsequent 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 creation of
Ontario County from Montgomery. The area split off from Montgomery County was much larger than the present county, as it was later divided to form the present
Allegany,
Cattaraugus,
Chautauqua,
Erie,
Genesee,
Livingston,
Monroe,
Niagara,
Orleans,
Steuben,
Wyoming,
Yates, and parts of
Schuyler and
Wayne counties. Jefferson County is part of
Macomb's Purchase of 1791. 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. The first one of these, in 1794, produced
Onondaga County. This county was larger than the current Onondaga County, including the present
Cayuga and
Cortland Counties, and part of
Oswego County.
Oneida County (as well as a part of
Chenango County), was split off from Herkimer County in 1798. Jefferson County was split off from Oneida County in 1805. In 1817,
Carleton Island, captured from the British in the
War of 1812, was annexed to the county. During the late eighteenth and nineteenth centuries, the county was largely developed for agriculture. By the early 20th centuries, Watertown was a city with the highest per capita number of millionaires in the United States. Local industrialists had made early fortunes from industries driven by water power. Mills were established along the falls of the Black River from the first half of the nineteenth century. In the nineteenth century there was considerable mining in the county, with iron (
hematite) being mined at the Sterling Mine (1850s), the Dickson Mine (1858), the Keene Mine, and the Shirtliff Mine (1860);
baryte at the Pillar Point Mine;
fluorite at Muscalonge Lake (1840s); and calcite at Blackriver. Limestone was quarried at Chaumont, Clayton, Cape Vincent and Watertown. By the end of WWI most mining in Jefferson County had ceased. ==Geography==