Betty Clark was born in Wrentham on Aug. 7, 1752, and moved with her parents and siblings to Keene, N.H., when she was about 7 or 8 years old. That winter, several residents of Keene came down with smallpox, and apparently Betty was one of them. She died on March 9, 1761.

The Clarks buried their daughter in a small cemetery near their home, and as time went on, the story of this little girl’s life became lost to history.

That changed one day in June, when Bill Fenton made a startling discovery as he was repairing the front steps of his house in Keene. Hidden inside the steps was Betty’s 256-year-old gravestone.

“Here lies buried Betty Clark...’’ the inscription read.

Thanks to his discovery, Betty Clark’s headstone has since been returned to its rightful place. On Tuesday, dozens of people gathered at Ash Swamp cemetery to pay respects to Betty Clark and her family and rededicate her gravestone that had been missing for centuries. “It was kind of serendipity that it was found in somebody’s steps,’’ said Rick Swanson, the development director of the Historical Society of Cheshire County.

Exactly how it ended up on Fenton’s property remains a mystery.

After the headstone was unearthed from the base of his front steps, he contacted the historical society and told them what he found.

Alan Rumrill, the historical society’s executive director, told Fenton that it’s not uncommon to come across a discarded gravestone. In most cases, the old stone has been replaced by a newer stone at the cemetery. Rumrill had expected to find that another gravestone had been made for Betty, but he couldn’t find any. He checked a listing of Keene burial sites that was compiled in the 1880s, and her name wasn’t there.

“In this case, we couldn’t find Betty anywhere,’’ he said.

After doing more research, he determined that the gravestone had originally stood in Ash Swamp cemetery, a small burying ground not far from Fenton’s home. The small cemetery sits on top of a little hill overlooking the Keene Country Club. It dates back to 1761 — the year Betty died — and was originally used as a burying place for smallpox victims. Rumrill said he has “no doubt’’ that Betty Clark was laid to rest there. “Her father and other family members were buried there, too,’’ he said.

Rumrill believes her headstone was removed from the cemetery sometime before 1880, because Betty’s name was not included in the 1880s list of burial sites. He said the headstone may have fallen over, and someone decided to remove it and incorporate it into the steps of Fenton’s house, which was built in 1820.

Emily Sweeney can be reached at esweeney@globe.com. Follow her on Twitter @emilysweeney.