Does my county fall under federal smog rules or breathe unhealthy air?

Among 203 counties EPA currently lists as nonattainment for ozone or fine particles, the largest are Los Angeles County, CA (10,013,976 residents), Cook County, IL and Harris County, TX.

Los Angeles County, CA10,013,976

Cook County, IL5,275,555

Harris County, TX4,731,122

Maricopa County, AZ4,425,102

San Diego County, CA3,298,648

Orange County, CA3,186,997

Kings County, NY2,736,119

Dallas County, TX2,611,481

Riverside County, CA2,418,182

Queens County, NY2,405,425

What it shows: Los Angeles County, CA is the largest at 10,013,976, followed by Cook County, IL at 5,275,555; the smallest shown is Queens County, NY at 2,405,425.

Source: EPA Green Book, Currently and previously designated nonattainment areas by county; county population from the 2020 Census · file downloaded 2026-09 (EPA export 2026-09-30)