Ms Maurissa Bickford, 39, pulled her son Noah out of the water and put him on top of the ice. But she was unable to lift herself out of the frigid waters, local broadcaster WHIO-TV reported.
The two were found unresponsive last Thursday by county highway garage employees Zachery Rogers and Samuel Deatherage who were working nearby the pond, reported The Daily Mail.
It is unclear how long the mother and son had been in the water. The pond is three metres deep.
The two men pulled Noah to a bank and administrated CPR while his mother was pulled out of the water by fire department workers.
They were both taken to nearby hospitals where they later died.
Shelby County Sheriff John Lenhart told WHIO-TV: "I can only imagine what she was going through when she saw her child in the water.
"She went in after him but there were no survivors, which is unfortunately very, very sad."
The pond is on the residential property of the family's neighbour John Moeller, reported NY Daily News.
He returned to his home just moments after the workers discovered the mother and son.
Mr Moeller said the pond could be used for recreation and fishing, and that kids were allowed in the pond as long as they were supervised by an adult.
He said the community was banding together to help Ms Bickford's husband and daughter.