There's New Zealand if you want more diversity.
78% European is diverse?
http://en.wikipedia.org/wiki/New_Zealand#Demography
And, we're talking about less than 4.5m people.
Compare it with http://en.wikipedia.org/wiki/Demographics_of_Chicago , which has more people than live in all of New Zealand's 4 largest cities and has almost as many people as NZ's 16 main urban areas. And, that's not counting Chicago's suburbs.
Chicago is only moderately diverse for a large American city - there are less than 50 languages spoken by more than 1000 people.
See http://en.wikipedia.org/wiki/Demographics_of_Los_Angeles for diversity (which has more people than all of new zealand's major urban areas, and I'm still ignoring suburbs and other major adjoining cities.)
And, they're about as diverse as Minnesota.