Pool season · Illinois
Decatur Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Decatur's whole pool calendar, condensed: when the water warms, when it cools, and where today falls between those edges. Use the opening guide and closing guide for the step-by-step work; keep this page for the dates.
Each dot on the bar is one week of Decatur's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (April 17–May 8), solid teal is swim season, and hollow amber is the closing window ending October 12. The black marker is today — its position against the colors is the entire executive summary.
The Decatur pool calendar
Opening — target April 24
Target April 24; the practical window runs April 17–May 8, and the 7-day mean crosses the 61°F threshold around May 8. Cold-water starts are the cheap ones.
Closing — deadline October 12
Hold the cover until October 2, then winterize by October 12, a week ahead of the October 24 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Decatur's typical-year water curve: the same EWMA model as the live widget, run on the 1991–2020 normals instead of this week's weather.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 28° | 28° | 37° | 48° | 59° | 69° | 75° | 75° | 71° | 61° | 48° | 36° |
The curve peaks near 76°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Decatur hits the closing window
Data: NOAA 1991–2020 climate normals via Decatur Wtp (2.1 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.