Clinton E. Smith made the plea Friday in Kalamazoo County Circuit Court. The plea means he won't face the possibility of a jury convicting him of first-degree murder.
First-degree murder bars parole, while second-degree murder includes the possibility of parole.
Judge Gary C. Giguere Jr. plans to sentence Smith on Feb. 18.
Police said Delores Mae Smith's body was found Sept. 12 in Portage after police responded to a request to check her welfare. She didn't show up for work that day.