The town began in 1735 as the fourth in a line of nine forts intended to protect southwestern New Hampshire from Indian attacks. The town was named for Johann Heinrich Alsted, a German professor whose Encyclopaedia (1630) was popular at Harvard, where Governor Benning Wentworth had been a student. According to the Towns municipal website, Alstead was one of the towns that wavered in its allegiance after the Revolutionary War. In April 1781 the citizens decided to join Vermont, but returned to New Hampshire authority early the next year. The town was also the location of New Hampshire's first paper mill, established in 1793 on the Cold River.

Population change totaled 1,056 over 56 years, from 843 in 1960 to 1,899 in 2016. The largest decennial percent change was a 41 percent increase between 1960 and 1970, close to one-third of the total numeric change. The 2016 Census estimate was 1,899 residents, which ranked 143rd among New Hampshire's incorporated cities and towns. (info from NHES website)Ⓘ