I thought they were a myth!
The New York Times has an interactive “Map of Baseball Nation” that uses Facebook (ugh) data to drill down into Major League Baseball fan preferences by ZIP Code.
Iowa is pretty much what you would expect. Most of the state puts the Cubs on top by a plurality, sometimes a heavy plurality. The bottom tier of counties has lots of Cardinals (east) and Royals (west) fans, and northwest of a Sioux City-Clarion-Decorah line there are a lot of Twins fans.
The northernmost tier of counties is the only place the Facebook data finds an outright majority in a county for one team, the Twins; in ZIPs along the Minnesota border the favorite cracks 60%. The Cubs are in the high 40s in far eastern Iowa. But in Allamakee County, we find an outlier: 41% root for the Brewers.
The Yankees are quite often the second- or third-most popular team in a given area, except around Council Bluffs and Glenwood, where they are #1. Western Iowa south of Sioux City is very fragmented between the Cubs, Yankees, and the other regional teams. As for all those counties in Nebraska where the Yankees are top dog…draw your own conclusions.
The Tama County breakdown is 33% Cubs, 12% Cardinals, 11% Twins.
While I have my doubts/suspicions about using Facebook data as a stand-in for statistical samples, it’s an interesting map, and I hope the NYT will do similar things for the NFL, NBA, and college teams.