Settled in 1726 by Scottish-Irish immigrants, the town was first named Coleraine. Fertile ground made it popular with farmers. It was later renamed Brookfield, after Brookfield, Massachusetts, and made a part of Middleton. But in 1785 Brookfield petitioned, unsuccessfully, to be set off from Middleton. This was due to the division of the original town of Middleton into two parts by the long, high ridge of Moose Mountain, then a considerable obstacle to travel. Town meetings, traditionally held in the muddy season of March, were particularly difficult to attend for those beyond the ridge. In 1794, however, permission was granted, and Brookfield incorporated. And in 1840, when Carroll County was set off from Strafford County, Brookfield went with Carroll, and Middleton remained with Strafford.

In 1874, the Wolfeborough Branch Railroad passed through this town.

According to the United States Census Bureau, the town has a total area of 23.3 square miles (60 km²), of which 22.9 sq mi (59 km²) is land and 0.4 sq mi (1.0 km²) is water, comprising 1.68% of the town. Brookfield is drained primarily by the Branch River and Pike Brook, within the Piscataqua River (coastal) watershed, though the western edge of the town is in the Merrimack River watershed and the northernmost tip of the town is in the Saco River watershed. Copple Crown Mountain, the highest point in Brookfield, has an elevation of 1,868 feet (569 m) above sea level.

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