The shooting happened as officers were conducting an investigation just before noon in the 11000 block of South Vernon Avenue, in the Roseland neighborhood, the Chicago Police Department said.
Police said a dog on a sidewalk was unleashed by its owner and approached the officer aggressively. One of the officers shot their weapon at the dog.
The condition of the dog was not immediately known.
Another officer had a leg injury from apparent debris. The officer was taken to a local hospital, initially reported to be in good condition, police said.
The owner of the dog was issued a citation for "Unleashed Dog."
Police continue to investigate.
No further information was immediately available.