Dublin Irish Festival, Dublin OH. I'd guess there were about 30,000 people there on the Saturday I attended, given the overall attendance numbers provided by the festival.

As soon as I get a kilt in Columbus Crew colors, I'll probably start wearing one to MLS games like McMurdo. Crew Stadium only seats about 20k, and usually has about 15k in attendance; quite a bit smaller than the Dublin Irish Festival.

However, I plan to get a kilt in Ohio State University colors to wear to football games; that'll push my number up to 105k, and probably 2-3 times that if you include the folks milling around the campus area for all the gameday partying. But that probably won't happen until next year.