Ronald Disher, 72, of Almond was charged with three felonies - fraud, forgery and theft - in an alleged scheme to fraudulently cash Marie Jost's Social Security checks for more than 30 years.
A jury Friday failed to reach a verdict on those counts following nearly nine hours of deliberations over two days.
The jury convicted Disher of two misdemeanors: endangering safety and disorderly conduct involving a confrontation with a Social Security investigator, WAOW-TV reported.
Portage County Assistant District Attorney Veronica Isherwood said she will seek a new trial on the felony counts.
Disher's attorney, Gary Kryshak, said he was disappointed with the mistrial.
"I am prepared to go at it again," he said.
After jurors told the judge that they couldn't agree on a verdict, Disher was returned to the Portage County Jail.
Jost was last seen in the 1980s. Prosecutors say some $170,000 worth of her Social Security checks were fraudulently cashed.
Disher was charged in the alleged check-cashing scheme with his wife, Delores, and brother-in-law, Charles Jost. Jost was found not guilty by reason of mental disease or defect and was sentenced to a mental institution. Charges against Delores Disher were dismissed after she suffered a stroke in jail.
In testimony Thursday, Ronald Disher said he had a fourth-grade education, could read "a little bit" and can write only his name and a date.
Disher said he earned money by selling iron and from a minnow business. He told the jury he never got any money from Marie Jost's Social Security checks.
Prosecutors dismissed one count of mail fraud against Disher before he testified.