The bones were discovered 3 feet underground Tuesday by crews working on gas lines in Anderson, Ind., The Indianapolis Star reported.
Experts say the remains may have been buried when the area was a graveyard in the mid-1800s.
Police Sgt. William Casey said the area may have been used as a short-term burial ground before the city had a permanent cemetery, the newspaper said.
Madison County Historian Stephen T. Jackson told the Star human remains were frequently transported in the 19th century and someone may have forgotten to move the bodies.