Shortest run time got me thinking what is the smallest venue that still is a "professional production"
One I can think of is "oh my sweet land" which is done in a kitchen, not sure how many seats were in there since i never saw it but it can't be that big
A nearby theater where I volunteer here in Palm Springs is fully "professional" (including AEA actors and a paid, but non-union crew). It has 80 seats. But it's moving to a 240-seat space in March. Absent a great deal of outside funding, there's only so much one can do with fewer than 99 seats.
No need to go to Chicago; there are dozens of sub-100 theatres in New York. Professional=paid, and that's pretty definitive. Smallest I can think of in New York that is in regular operation is probably Under St Marks, less than 50. The small space at Cherry Lane is about 60 I believe.
I'm an actor and I've acted in spaces with 25 seats before (in my more precious, younger days). Funny to imagine us saying "it's a full-house tonight" when 25 people were there. And yes, we played to not-full houses many times.
One of the most riveting nights of theatre that I ever attended was about 15 years ago in Chicago at the State Street entrance of the Harold Washington Library - Chicago's main library.
OK, it wasn't really theatre, but it was a man and a woman debating the pros and cons of the library providing free access to unlimited porn on its computers.
I was the only sidewalk audience member listening to their words for a solid 90 minutes. Sometimes, he would argue the pros, but later the cons. And she would first argue the cons, yet later the pros.
If you are an adult with a Chicago library card, you may use any one of 150 computers on the library's third floor for up to 2 hours daily. Children are not permitted in this area.