^^
Canyon County Idaho = 12.0% poverty (right on the national average)
Caldwell city = 16% poverty, a little higher (28% Mexican in this town, so they more than likely account for the majority of that 16%)
Nampa city = 12.4% poverty
As for violence/gangsterness etc. I can't speak on it, but I'd imagine it's pretty infrequent like it is in Aberdeen despite the fact Aberdeen is, as Tadou pointed out, poorer than the urban areas in the Northwest.
I'm not some fucking genius, I just know where to look:
US Census Bureau American FactFinder