The plea came in the form of a bill of information, meaning Cornwall waived indictment by a grand jury and accepted responsibility.
The robberies occurred on June 10 and June 11.
Cornwall faces a maximum of 12 years in prison. Judge Jennifer McElfresh set sentencing for Oct. 10.
Middletown police say Cornwall passed a note to a cashier at the Oxford State Road store, stating, “Put all the money in the bag or I’ll shoot you. I have a gun,” according to the Butler County Sheriff’s Office report and court documents.
The note was passed after a suspect asked a bagger to get some peanut butter he had forgotten. The cashier said she did not know what to do so she gave him back the note and walked away.
The suspect was seen fleeing the store wearing all black, a mask and blue gloves. He did not get any money, according to the report.
He was also seen leaving the parking lot in a white sedan going east on Oxford State Road.
Minutes later, a Middletown police officer spotted a similar car in the city, which was reported stolen and like one used in other area Kroger robberies. The officer tried to make a traffic stop at Waite and Sherman streets, but the driver refused to stop and took off on University Boulevard.
After a chase with speeds more than 80 miles per hour, the driver attempted to make a turn onto Breiel Boulevard but crashed in the median, according to police and court complaints.
Cornwall, fled on foot toward a nearby high school and was chased by officers and a K-9 called Bear, who “subdued” him, according to police.
Sheriff’s deputies searched the reportedly stolen car Cornwall was driving and found a facial covering and notes similar to the one the cashier described. After treatment for a dog bite, he was booked into the city jail.