Williams has been living in a group home for years under the name John D108 Doe, the Detroit Free Press reported. He was identified after the newspaper ran a story about him.
His cousin, Olivia Williams, said the family filed missing persons reports and tried to trace him. They believe he wandered away after his mother, Mary Brown, died.
Relatives say Williams became less and less verbal as he grew older.
Kathleen White-Montgomery, who has been Williams' legal guardian since May, said she is unsure when he will meet his relatives. She said he may not recognize them and is also uncomfortable in groups of strangers, so she hopes for a gradual reunion.