Visit a local elementary school and you'll see what I mean.
You are so right. The San Ysidro Health Center is located near the border within the city of San Diego (San Ysidro is part of San Diego). Its patrons are at least 90% Mexican. San Ysidro High School, nearby, is 85% Mexican. Of course this is near the border but further north, in certain areas, the majorities are almost as large.
I took my son to the Conroe Clinic about 30 miles north of Houston. It was 99% Hispanic except for us and I think we were the only ones paying.