Chicago, August 26 - 29

Later that month anti-war protests took place in Chicago, Illinois during the Democratic National Convention, and a massive force of law enforcement (Chicago Police with assistance from over 6,000 National Guard members and 6,000 Army troops (Taylor and Morris 2018)) responded excessively, including with chemical weapons, on network news (Schultz 1969; Karnow 1983; Farber 1988; Langguth 2000). After four days, hundreds had been given medical assistance for exposure to chemical weapons (Taylor and Morris 2018).

Although I have yet to find contemporary documentation of fogger use during the convention, an AP report on fogger use in Berkeley the year later states

A similar device was used during demonstrations in Chicago during the Democratic convention last summer. - Associated Press (1969f)

As such, I consider this a very likely deployment. I am continuing to search for evidence.