Pool season · Illinois
Chicago Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
One bar, one year, one Chicago pool. The season bar below draws everything the model knows — opening window, prime season, closing window — against today's date, with the working details one click away on the opening and closing pages.
Chicago, IL — 48 swim days a yearReading it takes ten seconds: 52 dots, one per week. Solid teal is Chicago's swim season; the hollow teal run before it (May 5 to May 26) is when to open; the hollow amber run after is when to close, with October 9 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Chicago pool calendar
Opening — target May 12
Open by May 12 — a two-week head start on the May 26 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 9
Hold the cover until September 29, then winterize by October 9, a week ahead of the November 5 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Chicago's own normals — the shape of a typical year, not a forecast. The widget above shows where the current year actually sits.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 27° | 27° | 34° | 43° | 53° | 64° | 72° | 74° | 71° | 60° | 48° | 36° |
The curve peaks near 74°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Champaign's pool season and Cicero's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Illinois season index.
Chicago pool season FAQ
When should I open my pool in Chicago, IL?
Target May 12. That date backs off two weeks from the day Chicago's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Chicago opening guide.
When should I close my pool in Chicago?
The closing deadline is October 9 — late enough that the water has cooled out of the algae zone, early enough to beat Chicago's first-freeze normal by about a week. See the Chicago closing guide for the winterizing steps.
How long is the swim season in Chicago?
Chicago averages 48 days a year with normal highs of 80°F or better — about 7 days later than the Illinois median. The Illinois season index ranks all 18 covered cities by the same metric.
How warm does pool water get in Chicago?
An unheated pool near Chicago typically peaks around 74°F in high summer and bottoms out near 26°F in winter, never quite reaching the 78°F comfort line without a heater or solar cover. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when Chicago hits the closing window
Data: NOAA 1991–2020 climate normals via Chicago Northerly Island (4.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.