The Chiefs have only played twice at Wrigley it looks like, in 2008 and 2010. I know there was also a game in recent years at Miller Park in Milwaukee between Appleton and somebody, too (either Peoria or Kane County, I think).
This happens a lot less often than it might seem. This game will only be the 8th time a Midwest League team has played in a MLB park according to this article, and the first time for a Quad Cities franchise. It's also the first time St. Louis has hosted a regular season game of any of their affiliates since 1992. It sounds like it is very difficult to work out the logistics. They've been trying to make this happen for 2 years.http://qctimes.com/news/local/article_3 ... 002e0.html