Jefferson County, NY
History
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.
Source: Wikipedia
Modern Day Adjacent Counties
St. Lawrence County – northeastLewis County – southeast
Oswego County – southwest
Leeds and Grenville United Counties, Ontario – north
Frontenac County, Ontario – northwest