400 dance club at the Trianon Ballroom in Chicago

Years back when the Trianon Ballroom in Chicago existed, there was a dance club called the 400. Does anyone know where the 400 number came from. Was that the number in the club or was it taken from some elite socialite group or whatever. Thanks Chuck 22

According to the stories of both my parents, both my mother and my aunt (her twin) were members of the Trianon 400 - an invitation-only group of the best dancers.

My uncle and my father (who were not members of the 400) both used to refer to my mom and aunt’s dancing skills with “Well, she was always a good dancer - she was one of the Trianon 400.”