I echo Michael Boo's comments about the old Ames Field in Michigan City.
Back in the day, there was an Illinois drum corps circuit (can't remember the exact name) that fielded very small, young corps and had competitions around the Chicago area. Some of those contests were in parks with portable bleachers brought in. I also attended a DCM show in a park in Rosemont sometime in the early 1990s.
But the most memorable was a DCI show in a little town south of Grand Rapids, Mich., I think it was 1996. Stands were old and wooden, about 10 rows high, perched on the bank of a creek. First part of the show was all small corps. But then the Crossmen came out and I literally thought those stands would tumble into that creek.