The shooting happened before 2 a.m. at a home in the 900 block of Oak Ridge Boulevard, Elgin police said.
An Elgin police officer responded to a report of a suicidal person and discovered a 29-year-old man with visible wounds. When the officer tried to help the man, he began to stab himself, according to police.
The man then turned his attention to the officer, who shot and wounded the man before giving the man medical aid.
The 29-year-old man was taken to a hospital and was reported to be stable.
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The officer has been put on administrative leave pending investigation, police said.
No further information was available.