First granted by the New Hampshire proprietors in 1752, the town was given the name Boyle, after Richard Boyle, Earl of Burlington and a distinguished architect. No claims were settled within the prescribed time because of danger from Indian attacks. A new charter was issued in 1763 to Benjamin Sumner, who surveyed the area and established a settlement along with several relatives from Connecticut. One of those settlers was Captain Samuel Gilbert, who became the first moderator. The name Gilsum was adopted in their honor. Gilsum's Lower Village is the site of the much-photographed Stone Arch over the Ashuelot River.
Population change for Gilsum totaled 269 over 56 years, from 528 in 1960 to 797 in 2016. The largest decennial percent increase was 17 percent between 1990 and 2000. The 2016 Census estimate for Gilsum was 797 residents, which ranked 197th among New Hampshire's incorporated cities and towns. this town has 47.8 persons per square mile of land area.(info from NHES website)