CNN Money lists the richest and poorest counties in the U.S:
1 Hidalgo County, TX
2 Cameron County, TX
3 Bronx County, NY
4 El Paso County, TX
5 St. Louis city, MO
6 Philadelphia County, PA
7 Caddo Parish, LA
8 Orleans Parish, LA
9 Baltimore city, MD
10 Mahoning County, OH
That's considering only counties with a population over 250,000.
I have lived in the first and fourth poorest counties, and am well familiar with the second, all on the Mexican border. That must qualify me for something.
Glad to be where I am now, although I did enjoy my time in El Paso. I've written about those other places in Texas here, here, and here.
I've lived in the Bronx, albeit only for a few months. And I've lived in Seattle, which is #8 on the richest. In both cases, I'd say that which neighborhood you lived in mattered far more than in which county, although the differences are -- last I looked, which is some years ago -- generally rather more dramatic in the Bronx than in Seattle.
Sorry: I conflated the county and city lists.
Ah, and I see that Kings County, aka "Brooklyn" is #18 on the poorest list.