LITTLE COMPTON — Female sachems for the local Indian tribe and colonist Benjamin Church joined forces in the 17th century during King Philip’s War along the land’s cobble shore.

A pastor used to row his boat across the Sakonnet River to give a sermon in a chapel in the farm’s main building.

And the block house in the middle of a cleared corn field — a remnant from the Revolutionary War — still has a part of a wall standing.

“With this much history, I feel a sense of responsibility to protect it,” said Josie Richmond Arkins, who owns the 116-acre Treaty Rock Farm off West Shore Road with her sisters Lawre Goodnow and Helen Richmond Webb.

The trio recently sold conservation easements for their farm — which has been in the Richmond family for more than 350 years — to the Little Compton Agricultural Conservancy Trust and other agencies. The $3.6-million agreement ensures the land remains a working farm and open coastal habitat.

The family and Trust plan to announce the agreement at a 10:30 a.m. news conference today at the farm’s barn, which was built in the early 1900s.

“We are very excited,” said Arkins, who is the only sibling still living on the property with her family, a chocolate Labrador, a dozen chickens, 16 sheep, 2 ponies, 50 cows and a donkey named Toby. She and her husband built a house attached to a silo, one of a few left in the area. They converted the silo into a storage site and bathroom.

Other buildings on the farm include the main house, which the sisters’ parents sold years ago. The owners, who Arkins didn’t name, have rights to the land their house sits on as well as the road leading up to their residence.

Yet the rest of the land belongs to the Richmonds. The majority is open to foster their farming business. They sell their beef locally. They also supply wool from their sheep to a statewide blanket project called “Rhody Warm.” That project was launched about two years ago by local farmers, state agencies and the Rhode Island Resource Conservation & Development Area Council.

Arkins continued, “We are very committed to maintaining a viable farm, to increasing the habitat and biodiversity on this property, and to preserving the rural and historic character of Little Compton.”

The sisters first discussed protecting the land 13 years ago and contacted the Champlin Foundations for assistance. After several options, the easement agreements were solidified. The Trust and Rhode Island Agricultural Lands Preservation Commission hold the deed to development rights for agriculture on 95 acres of the farm. The Nature Conservancy holds a conservation easement over about 20 acres of land and tidal zone along the Sakonnet River.

Money for the purchase came from several sources: including the Trust, the Conservancy, state farmland protection bonds, the Champlin Foundations, the Sakonnet Preservation Association, the federal Department of Agriculture Farm and Ranch Land Protection Program and many private donors.

The groups involved say the purchase price is a “bargain sale” due to the “high value of all developmental rights” on the farm, a news release states.

“The owners’ commitment to conservation coupled with our efforts and those of our partners have ensured that historic Treaty Rock Farm remains an open landscape with agricultural use,” said Trust chairman George Mason.

Janet Coit, director of the state’s chapter of the Nature Conservancy, said, “Our local farms, wildlife habitat and beautiful shoreline are some of Rhode Island’s greatest assets and need to be protected for the future.”

apina@projo.com