Pool season · State index
Illinois Pool Season Calendar
Last updated: July 15, 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.
| 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.