The physical description and clothing on the body discovered Sunday in Millington, about a half-hour north of Memphis, matched that of Aniston Walker, who was reported missing Jan. 9, police said in a news release.
Police did not say how the baby died. An autopsy was being conducted Monday.
The baby's mother, Andrea Walker, told police that Aniston disappeared after she left the baby at home with her 3-year-old child while taking her 5-year-old child to school.
Police said Walker called the child's father, who does not live at the same address, and he reported the baby missing. Walker then left the house again - leaving the 3-year-old alone in the house for an hour - as she traveled to several locations around the city.
Police Director Toney Armstrong said at the time that Walker was not as forthcoming with investigators as they could have wished.
Before Aniston's body was discovered, Walker had pleaded not guilty to charges of aggravated child abuse or neglect. She was free on $250,000 bond before she turned herself in on Monday.
Calls to Walker's attorney were not immediately returned.
Back in January, police searched for the baby for three days with no results. Then on Sunday, a motorcyclist stopped on the side of the road in Millington saw the child's body in a ditch and called police.
"It is heartbreaking to confirm that an innocent child's life has been taken," Armstrong said in a statement, "but now family members of Aniston Walker can have closure and begin the healing process of losing a loved one."
Andrea Walker was charged with two counts: first-degree murder in the perpetration of a felony, to wit, aggravated child neglect or endangerment; and first-degree murder in the perpetration of a felony, to wit, aggravated child abuse.