Northfield, IL
Above the federal action level
Latest 90th-percentile lead: 21 ppb (monitoring period 2026-2026). The federal action level is 15 ppb today and drops to 10 ppb in Nov 2027; EPA's health goal is 0. In the most recent monitoring period, more than 10% of the sampled homes measured above 15 ppb. Use a filter certified to NSF/ANSI 53 for lead for drinking and cooking now, and test your own tap.
About Northfield
Northfield serves about 5,751 people through 2,055 service connections, which makes it a medium-sized system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws surface water, in Cook County, Illinois. EPA system ID: IL0312100; phone on file: 847-784-3581. They can tell you what your service line is made of and whether they pay to replace it.
Northfield's lead record
That is up 19.6 ppb from 1.4 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for Northfield is 21 ppb across 7 monitoring periods, 2 of them over the 15 ppb action level.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 21 ppb over 15 |
| 2025 | 1.4 ppb |
| 2025 | 17 ppb over 15 |
| 2025 | 7 ppb |
| 2023 | 3.4 ppb |
| 2020 | 3.8 ppb |
| 2017 | 7.2 ppb |
Against other Illinois systems
Of the 1,744 Illinois systems with a lead result, the median latest reading is 0 ppb; 22 are over 15 ppb right now and 152 have gone over at some point. Northfield's 21 ppb sits at the 99th percentile in Illinois and the 99th nationally (higher means more lead).
Neighbouring systems
154 other systems share Cook County; 1 of them has a higher latest lead result than Northfield. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Chicago | 2,721,308 | 6.4 ppb |
| Cicero | 83,000 | 5 ppb |
| Schaumburg | 75,750 | 0.87 ppb |
| Evanston | 74,486 | 6.5 ppb |
| Arlington Heights | 73,320 | 7.6 ppb |
| Palatine | 70,875 | 8.9 ppb |
| Skokie | 66,422 | 9.77 ppb |
| Des Plaines | 60,675 | 5.7 ppb |
| Oak Lawn | 58,362 | 9.3 ppb |
| Orland Park | 58,020 | 0 (not detected) |
What to do in your house
Use a filter certified to NSF/ANSI 53 for lead on the tap you drink and cook from, now, before you test. Then test your own tap. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Northfield whether it covers that cost before hiring anyone - many utilities now do.
These figures describe homes the utility sampled, not your tap. Only your service line record or a test of your own water answers the question for your house. Why sampled homes are the worst-case ones is in the guide to reading the number. The action level is dropping - the 10 ppb rule from 2027.