ASHFIELD — The Hilltown Land Trust, founded in 1986 by a small group of volunteers, has achieved national accreditation, joining fewer than 300 such land trusts nationwide.

The trust, which serves 13 towns west of the Connecticut River, has protected over 3,700 acres, including the Bradley and Breckenridge sanctuaries in Williamsburg and the Stevens Hiking Trail in Huntington.

To earn accreditation, a land trust must demonstrate excellence in its operations, show that it upholds the public trust, and ensure that its conservation efforts are permanent, said land trust director Sally Loomis. Each accredited land trust must submit extensive documentation and undergo a rigorous review.

“The Hilltown Land Trust has worked hard to bring our policies and practices to the highest levels required for accreditation,” said Loomis. “We have learned so much through the rigorous program, and are now a stronger, more efficient and productive organization.”

The evaluations are conducted by the Land Trust Accreditation Commission, an independent program of the national Land Trust Alliance. Only ten of 137 land trusts in Massachusetts have earned national accreditation.

Board president Marie Burkart noted that for most of its history, the land trust undertook its conservation work with a small group of knowledgeable volunteers. She said the accreditation reflects well upon not only upon those volunteers, but the organization’s small and dedicated staff.

The Hilltown Land Trust in 2010 became affiliated with The Trustees of Reservations, a Boston-based land conservation organization and the oldest land trust in the country.

Earlier this month the land trust sponsored a hike from the Bullitt Reservation to Chapel Falls through the wooded hills of Ashfield; similar events are planned all winter long.