The first documented inhabitant of what would become the Town of Clarksburg was a Soldier from Fort Massachusetts named Seth Hudson (hence the Hudson Brook naming)in 1749, when he felled a tree just North of Natural Bridge. He went on to later help found the neighboring Town of Pownal, Vermont.
Captain Matthew Ketchum, Colonel William Bullock, and Nicholas Clark are credited with having originally settled the eventual township in 1769, and the latter ultimately became Clarksburg's namesake due to the birth of a child, thus giving the Clarks one additional vote in the naming of the Town. The town began as a mostly agrarian community, with mills springing up along the waterways in the nineteenth century. The major mills were one to make cashmere, and several mills supplied gunpowder during the Civil War. However, the industry was stopped by the town after one of the mills exploded in 1869 in the area of what was "Sunnysides Lounge", and that section of Town was known for many years as "Powdermill Flats".
Clarksburg was first settled in 1769 by Captain Matthew Ketchum, Nicholas Clark and others. It is related when Colonel William Bullock measured out the grant which bears his name he was compelled, in order to complete his complement of 23,000 to extend it around Bernardston's grant. He intended to reach the Vermont line, but not knowing where it was, and careful not to lose any part of his grant by going into that State, he stopped a mile short of the line, and proceeded westward four or five miles along the north line of Bernarston's grant and [North] Adams. The part of Bullock's grant which lies north of this grant and town and west of Monroe, together with the gore which separates it from Williamstown and Vermont, originally constituted Clarksburg. A part of it was annexed to Florida [MA] on May 2, 1848. originally, the Town contained 10,400 acres. As early as 1829 there were four mills running all year round. Briggsville, where the earliest post office in the Town was established and had A.A. Lee for its Postmaster. Clarksburg was officially incorporated in 1798.
According to the United States Census Bureau, the town has a total area of 12.8 square miles (33 km), of which 12.8 square miles (33 km) is land and 0.1 square miles (0.26 km) (0.62%) is water.
The town is bordered on two sides by mountains, with East Mountain and Bald Mountain to the west, and the Hoosac Range to the east. Between the two ranges, Hudson Brook and the north branch of the Hoosic River flow through the valley, merging just south of the town line. In the northern part of the valley is Clarksburg State Park, operated by the state's Department of Conservation and Recreation. The park is home to Mauserts Pond and offers picnicking, hiking, and camping, as well as other recreational activities. On the Vermont side of the border lies the Green Mountain National Forest. The Appalachian Trail crosses from north to south through the town, passing just west of the peak of East Mountain, the highest point in town, at 2,300 feet (700 m)..