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Counties → Illinois

Cook County, Illinois

SDWIS compliance plate

Sheet IL031 · Cook County 427 sys · 21,728 viol · #4/3254

VIOL-SEVERE · HEALTH-LOW · RANK-TOP · PHOTO-FINISH · PFAS-LOW · SRC-SW · SYS-LARGE · BOOK-FULL

  • VIOL-SEVERE 70.5% flagged
  • HEALTH-LOW 8.7% health
  • RANK-TOP #4/3254
  • PHOTO-FINISH ±0.1 pp
  • PFAS-LOW 6.1% detect
  • SRC-SW SW lead 54%
  • SYS-LARGE 427 systems
  • BOOK-FULL 7/7 fields

Nearest flagged-rate peer: Lake County ( -0.1 pp flagged-rate)

According to EPA SDWIS county population served used on /counties, Cook County ranks #4 of 3,254 counties by people served, and #1 of 102 counties in Illinois. See methodology · corpus placement.

Cook County standing, lower-flagged corpus third

Flagged-system rate 70.5% is at or below the corpus lower third (≤ 92.7% flagged) across 2,973 counties with ≥3 SDWIS systems . Health-based share 8.7% is health-based share at or below the lower third (≤ 10.3%) . UCMR5 detect rate 6.1% is UCMR5 detect rate in the tested-pool middle third (≤ 33.3%) . Population served ranks #4 of 3,254 · #1 of 102 in Illinois.

Flagged-rate neighbourhood around Cook County

Lowest/highest poles plus in-state counties nearest Cook County on % of SDWIS systems with ≥1 violation. Full ladder: /counties.

0% 20% 40% 60% 80% 100% Sangamon · lowest Lake · near Iroquois · near Pulaski · highest 58.8% 70% 70.4% 70.5% 71% 71.4% 100%

Source: EPA SDWIS (county aggregates) As of 2026-05-15

Water Systems

System Name Population Violations PFAS
Chicago 2,746,388 212 Clean
Cicero 83,000 43 Clean
Schaumburg 75,750 22 Clean
Evanston 74,486 99 Clean
Arlington Heights 73,320 79 Clean
Palatine 70,875 28 Clean
Skokie 66,422 26 Clean
Des Plaines 60,675 17 Clean
Orland Park 58,862 20 Clean
Oak Lawn 58,362 39 Clean
Berwyn 57,250 70 Clean
Tinley Park 56,703 42 Clean
Oak Park 54,583 29 Clean
Hoffman Estates 50,179 42 Clean
Glenview 47,856 29 Clean
Buffalo Grove 43,212 13 Clean
Bartlett 41,500 300 Clean
Mount Prospect 41,000 49 Clean
Park Ridge 39,800 19 Clean
Wheeling 39,725 43 Clean
Streamwood 39,577 27 Clean
Hanover Park 37,470 102 Clean
Calumet City 37,000 64 Detected
Elk Grove Village 34,700 41 Clean
Northbrook 34,407 25 Clean
Aqua Illinois-North Maine Utilities 30,043 89 Clean
South Stickny SD 30,000 73 Clean
Niles 29,350 23 Clean
Lansing 29,076 33 Clean
Oak Forest 27,478 24 Detected
Wilmette 27,087 26 Clean
Chicago Heights 26,184 40 Clean
Morton Grove 25,297 23 Clean
Elmwood Park 25,000 39 Clean
Harvey 25,000 41 Clean
Melrose Park 24,206 132 Clean
Maywood 24,090 104 Clean
Rolling Meadows 23,329 36 Clean
South Holland 22,000 37 Detected
Park Forest 21,975 154 Clean
Blue Island 21,494 23 Clean
Dolton 20,510 83 Clean
Evergreen Park 19,943 10 Clean
Homewood 19,463 22 Detected
Bellwood 19,156 53 Clean
Alsip 19,063 22 Clean
Brookfield 18,776 48 Clean
Palos Hills 18,530 18 Clean
Franklin Park 18,467 41 Clean
Justice-Willow Springs Water Commission 18,457 26 Clean

Compare beyond Illinois

Lower-flagged peers for Cook County

Cross-state counties nearest Cook County on flagged-system share (70.5%) and cumulative violation count (21,728). In-state neighbours stay on the compliance plate above.

Similar flagged-system rate

Nearest cross-state counties by % of SDWIS systems with at least one violation on record.

4 peers

Similar violation load

Nearest cross-state counties by cumulative SDWIS violation count (all systems in the county).

4 peers

Read our methodology · Check your water system - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.