I'd actually looked for this before, but just stumbled across it today: what's likely the first aerial footage of Chicago, shot by Harold Fowler McCormick, Jr.—grandson of Cyrus McCormick on his father's side and John D. Rockefeller on his mother's. The National Archives indicate that it was shot in 1926.

Bonus! Italo Balbo's triumphant greeting in Chicago in 1933, accompanied by aerial footage shot from the massive sortie that gave his visit some of that military flair. Years later, this would be really embarrassing.