An American Revolution-era flag was unveiled on Monday in the Castle Island exhibit at the Commonwealth Museum on Columbia Point. It will be on temporary display in Dorchester until mid-August.

The 13-star banner, which many experts believe is approximately 230 years old and was possibly in use at South Boston’s Fort Independence, is one of “less than a [handful] of American flags from this time period,” according to owner James Mooney.

“This is a very gratifying day for our family,” Mooney said in a statement. “We are very grateful to the Commonwealth Museum for making it possible for the people of Boston to know of, and see, this important relic from our nation’s earliest days.”

Mooney, who owns and operates a used manufacturing parts business in Cincinnati, inherited the flag from his mother. Mooney’s great-great-grandfather, John O’Callahan, discovered the flag after purchasing a fully-furnished Medford home in 1901 from a widow named Mrs. White. O’Callahan dusted off an old box labeled “great-great-grandad’s war flag” and found the banner inside, Mooney said.

“The condition of his flag is actually very good, which is a nice thing to see,” said Rabbit Goody, a textile historian who examined Mooney’s flag six years ago. “It’s difficult to know beyond a shadow of a doubt when the flag was in use, but we look for clues that help to place it in a larger material culture: How it’s put together, how it’s flown. …That said, there’s nothing in the construction, the fiber, or any of the textiles in the flag that could not have been produced in the 18th century.”

Mooney believes his family’s flag, which has tatters and frays on the corners and a sizable chunk missing from the bottom two stripes, has been overlooked by historians.

When asked by a reporter how many scholars are aware of the flag’s existence, he said, “Not as many as should, which is why we brought it here.”

“We hope,” he added, “that it can remind Bostonians of their history and inspire a patriotism in them.”