Pool season · Illinois
Alton Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
One bar, one year, one Alton 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.
The bar compresses Alton's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the April 10–May 1 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends October 18. Wherever the today marker sits, the nearest color change is your next appointment.
The Alton pool calendar
Opening — target April 17
Open by April 17 — a two-week head start on the May 1 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 18
Hold the cover until October 8, then winterize by October 18, 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 Alton'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 32° | 32° | 40° | 51° | 61° | 71° | 77° | 78° | 74° | 64° | 51° | 40° |
Warmest water typically August–August (peaking near 78°F); heaters and covers shift any month up.
Email me when Alton hits the closing window
Data: NOAA 1991–2020 climate normals via Alton - Melvin Price L&d (2.5 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.