I'll jump in on this (Iowa State grad). I live in northeast Iowa and there are a lot of Hawkeye fans up here. Most of the Iowa State fans are those that graduated or have kids at ISU. I notice that many who do NOT have any kids [or affiliation] at or that attended Iowa tend to lean and root for Iowa [along with Iowa grads]. Seems to be the trend in eastern Iowa. In western Iowa the trend is just the opposite.. fans tend to lean towards the Cyclones. Remember ISU had 36,660 enrolled in 2016 and Iowa had 33,334 enrolled. I would bet it's pretty close to 50/50 for the entire state. If you just live in eastern Iowa you would think that it's 99% Iowa and 1% ISU. Both GREAT schools with great rivalries.
50/50? Well, you are definitely a cyclone fan.
Also, enrollment doesn't equate to "fandom." Now I can't quantify this, at all, by my anecdotal experience is that I've met and discussed the varying Iowa colleges/universities with people over the years and when they don't attend Iowa (like attending ISU) there are still many, many that are fans of Iowa, and I don't see the opposite trend at all. To put more simply: Attending ISU =/= ISU fan, plenty are still Iowa fans. This happens more often with UNI and then smaller schools.
Now, admittedly this is likely due to the "embarrassment" factor, so it comes up far more when discussing football and wrestling than, say, basketball.
My opinion? Not close to 50/50, maybe 65/35, but many ISU fans refuse to "count" a lot of the Iowa fans because they call them "tavern" Hawks or just denigrate them in general for not attending any of the schools.
But in DM? A whole lot of ISU vanity plates, and the ISU crowd in the metro is very proud - go to the Jordan Creek mall on a weekend and garish red and yellow everywhere. They are very noticeable, imo, because they are college grads with good jobs and afford to flaunt it (such as vanity plates). But even then I doubt DM it is 50/50, and it is only a half hour from the school. That being said - the cesspool that is Ankeny is full of 'em.