Coös County, New Hampshire: History
Coös County was separated from the northern part of Grafton County, New Hampshire, on December 24, 1803, with its Superior Court established in Lancaster.
During the American Revolutionary War, two units of troops of the Continental Army — Bedel's Regiment and Whitcomb's Rangers — were raised from the settlers of Coös. From the Treaty of Paris of 1783 until 1835, the boundaries in the northern tip of the county (and New Hampshire itself) were disputed with Lower Canada (which was soon to become part of the Province of Canada), and for some years residents of the area formed the independent Republic of Indian Stream.
In the 1810 census, there were 3,991 residents, and by 1870 there were nearly 15,000, at which point the entire county was valued at just under $5 million, with farm productivity per acre comparing favorably with that of contemporary Illinois. Other early industries included forestry and manufacturing, using 4,450 water horsepower in 1870.