Pool opening · State guide
When to Open Your Pool in Illinois
Last updated: July 15, 2026 · 18 cities covered
Illinois's opening calendar spans about 27 days. The earliest model date belongs to Alton (April 17), the latest to Waukegan (May 14), and the statewide median lands on May 4.
Every date is the same model — two weeks ahead of the day the local 7-day mean temperature crosses 61°F — applied to each city's own NOAA normals station. Click through for the live water estimate, the full window, and the 12-step checklist.
| City | Open by | Window opens | 61°F crossing |
|---|---|---|---|
| Alton | Apr 17 | Apr 10 | May 1 |
| Arlington Heights | May 6 | Apr 29 | May 20 |
| Aurora | May 4 | Apr 27 | May 18 |
| Bloomington | Apr 30 | Apr 23 | May 14 |
| Champaign | Apr 26 | Apr 19 | May 10 |
| Chicago | May 12 | May 5 | May 26 |
| Cicero | May 1 | Apr 24 | May 15 |
| Decatur | Apr 24 | Apr 17 | May 8 |
| Elgin | May 7 | Apr 30 | May 21 |
| Evanston | May 12 | May 5 | May 26 |
| Joliet | May 5 | Apr 28 | May 19 |
| Naperville | May 8 | May 1 | May 22 |
| Peoria | Apr 25 | Apr 18 | May 9 |
| Rockford | May 4 | Apr 27 | May 18 |
| Round Lake Beach | May 11 | May 4 | May 25 |
| Schaumburg | May 6 | Apr 29 | May 20 |
| Springfield | Apr 26 | Apr 19 | May 10 |
| Waukegan | May 14 | May 7 | May 28 |
Dates are typical-year model outputs, not forecasts — each city guide carries the live widget that tracks the current year against them.
How to use these dates
Each "open by" date is two weeks ahead of that city's own 61°F crossing — the day its 7-day mean temperature (highs and lows averaged, from the nearest NOAA 1991–2020 normals station) reaches the level where unheated pool water starts climbing toward the 65°F algae-growth zone. Opening inside the window means starting up in cold, algae-resistant water: a single label-dosed shock instead of a green-water recovery, and a shopping trip while Illinois stores are still fully stocked.
Dates are typical-year guidance, not forecasts. A warm or late spring shifts the real-world moment by a week or two in either direction — every city guide carries a live water-temperature widget that tracks the current year against these normals, plus the full 12-step opening checklist sequenced to its local window. New to the process? Start with the generic how-to-open guide and the chemicals shopping list, then come back for your city's dates.