40 CFR § 52.721 - Classification of regions.

---
identifier: "/us/cfr/t40/s52.721"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 52.721 - Classification of regions."
title_number: 40
title_name: "Protection of Environment"
section_number: "52.721"
section_name: "Classification of regions."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "52"
part_name: "APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401"
cfr_part: "52"
---


# 52.721 Classification of regions.

The Illinois plan was evaluated on the basis of the following classifications:

|  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
| Burlington-Keokuk Interstate | I | I | III | III | III |
| East Central Illinois Intrastate | III | II | III | III | III |
| Metropolitan Chicago Interstate (Indiana-Illinois) | I | I | I | I | I |
| Metropolitan Dubuque Interstate | I | III | III | III | III |
| Metropolitan Quad Cities Interstate | I | III | III | III | III |
| Metropolitan St. Louis Interstate (Missouri-Illinois) | I | I | III | I | I |
| North Central Illinois Intrastate | II | IA | III | III | III |
| Paducah (Kentucky)-Cairo (Illinois) Interstate | I | II | III | III | III |
| Rockford (Illinois)-Janesville-Beloit (Wisconsin) Interstate | II | III | III | III | III |
| Southeast Illinois Intrastate | III | II | III | III | III |
| West Central Illinois Intrastate | I | IA | III | III | III |

[37 FR 10862, May 31, 1972, as amended at 39 FR 16346, May 8, 1974; 45 FR 11493, Feb. 21, 1980]