The primary settlement in town, where 1,094 people resided at the 2010 census, is defined as the Marlborough census-designated place (CDP) and is located at the junction of New Hampshire routes 101 and 124.
First granted as Monadnock No. 5 in 1752 by Governor Benning Wentworth, this was one of the fort towns originally known only by a number. Lots were drawn in 1762 and first settled two years later. The town was at one time called Oxford, then New Marlborough, but was incorporated in 1776 as Marlborough. Many of the settlers were from Marlborough, Massachusetts, which had been named for John Churchill, 1st Duke of Marlborough, in the late 17th century. Land was set off in 1815 to create the town of Troy.
There was once an important granite industry here. Stone from Marlborough quarries was used in buildings in Boston, at the College of the Holy Cross in Worcester, Massachusetts, and locally in the Frost Free Library. Blankets and wooden-ware, including toys, have been manufactured in Marlborough as well.