Pittsburg is a town in Coös County, New Hampshire, United States. The population was 800 at the 2020 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.

The Republic of Indian Stream or the Indian Stream Republic was an unrecognized republic in North America, along the section of the border that divides the current Canadian province of Quebec from the U.S. state of New Hampshire. It existed from July 9, 1832, to August 5, 1835. Described as "Indian Stream Territory, so-called" by the United States census-taker in 1830, the area was named for Indian Stream, a small watercourse. It had an organized elected government and constitution and served about three hundred citizens.