The other women held captive with her, Amanda Berry and Gina DeJesus, had been previously released.
Knight, now 32, was the first of the women kidnapped, having gone missing in 2002, The (Cleveland) Plain Dealer reported Friday.
In announcing Knight's release, a hospital spokesman said she had asked for her privacy to be respected and that she not be contacted.
The hospital also issued a statement for Knight:
"Michelle Knight is in good spirits and would like the community to know that she is extremely grateful for the outpouring of flowers and gifts. She is especially thankful for the Cleveland Courage Fund. She ask that everyone please continue to respect her privacy at this time."
Knight's disappearance had not received much attention because police and family members believed she had left on her own after she lost custody of her son.
Barbara Knight, Michelle's mother, returned to Cleveland this week from Florida, but has not been able to find out from officials where her daughter is, said Jay Milano, an attorney representing Barbara Knight.
"We just hope she's in a safe place, in a controlled environment, where she can decompress from all of this," Milano said.