Pittsburg is a town in Coos County, New Hampshire, United States. The population was 869 at the 2010 census. It is the northernmost town in New Hampshire and the largest town by area in New England. U.S. Route 3 is the only major highway in the town, although the northern terminus of New Hampshire Route 145 also lies within Pittsburg.
Pittsburg is part of the Berlin, New Hampshire–Vermont Micropolitan Statistical Area.
Pittsburg derives its name from William Pitt, Prime Minister of the United Kingdom. Prior to its incorporation in 1840, the area was settled c. 1810 and known as the Territory of Indian Stream. It had the unique distinction of having been its own microstate briefly during the 1830s, called the Republic of Indian Stream, due to an ambiguous boundary between the United States and Canada.
The Indian Stream Schoolhouse on Tabor Road, which dates to 1897, is listed in both the National Register of Historic Places and the New Hampshire State Register of Historic Places; the town hall on Main Street, which dates to 1883, is listed in the State Register.
Pittsburg shares an international border with Québec province, Canada to its west and north, and borders the states of Maine (to the east) and Vermont (a very small portion to the southwest). Directly to the south is Clarksville.