Pool season · State index
Illinois Pool Season 2026: Opening & Closing Dates by City
Last updated: July 25, 2026 · 18 cities covered
Both halves of the pool year for all 18 covered Illinois cities. The median calendar runs May 4 to October 7. Every row links to a one-page season overview with the live water-temperature model; the opening and closing hubs carry the full checklists.
Illinois: a moderate-season pool state| City | Open by | Close by | 80°F+ days |
|---|---|---|---|
| Alton | Apr 17 | Oct 18 | 106 |
| Arlington Heights | May 6 | Oct 7 | 75 |
| Aurora | May 4 | Oct 7 | 82 |
| Bloomington | Apr 30 | Oct 8 | 103 |
| Champaign | Apr 26 | Oct 11 | 102 |
| Chicago | May 12 | Oct 9 | 48 |
| Cicero | May 1 | Oct 12 | 84 |
| Decatur | Apr 24 | Oct 12 | 95 |
| Elgin | May 7 | Oct 4 | 80 |
| Evanston | May 12 | Oct 5 | 73 |
| Joliet | May 5 | Oct 7 | 81 |
| Naperville | May 8 | Oct 4 | 84 |
| Peoria | Apr 25 | Oct 11 | 101 |
| Rockford | May 4 | Oct 4 | 81 |
| Round Lake Beach | May 11 | Oct 2 | 65 |
| Schaumburg | May 6 | Oct 4 | 99 |
| Springfield | Apr 26 | Oct 11 | 96 |
| Waukegan | May 14 | Oct 3 | 48 |
What the columns mean
"Open by" is the recommended spring date — two weeks before the city's 7-day mean temperature crosses 61°F, the model's proxy for water approaching the 65°F algae-growth zone. "Close by" is the fall deadline — ten days after the water leaves that zone, capped a week ahead of the local 50% first-freeze date. "80°F+ days" counts days whose normal high reaches 80°F: the length of the true warm-swim season, and the fairest single number for comparing Illinois cities against each other.
Every figure comes from each city's own NOAA 1991–2020 normals station (named in its guide's footer), so neighboring cities can legitimately differ by a few days. The season overview linked from each row adds the live water-temperature model and the full-year season bar; the state hubs above carry the step-by-step checklists.
Swim-season length across Illinois
The fairest way to compare Illinois cities is the number of days with 80°F+ normal highs — the practical warm-swim season. Every bar links to that city's one-page season overview with the live water model.
Illinois pool climate at a glance
A tale of two states: chilly Lake Michigan keeps Chicago springs cool and openings late, while far southern Illinois warms weeks earlier with a near-Southern summer. In model terms that makes Illinois a moderate-season state. The spread shows up clearly on the local pages: compare Alton's pool season with Aurora's and the difference is measured in weeks, not days. Neighbors in the index run on their own normals too — see Idaho and Indiana for the adjacent calendars.
Illinois pool season FAQ
When do pools open in Illinois?
Model openings in Illinois run from April 17 in Alton to May 14 in Waukegan, with the statewide median on May 5. Each date is two weeks before that city's 7-day mean temperature crosses 61°F — early enough to start up in algae-cold water.
When should you close a pool in Illinois?
The median Illinois closing deadline is October 7, and every city's own deadline is capped a week ahead of its NOAA 50% first-freeze date. Closing late and cold beats closing early and warm — cool water holds its winter chemistry far better.
Which Illinois city has the longest swim season?
Alton leads with 106 days of 80°F+ highs per year, while Waukegan brings up the rear at 48 days. The chart above ranks every covered city by the same metric.