Illinois Pool Season: Opening & Closing Dates by City

Local dates for every featured Illinois city — when the water warms up, when it cools off, and how long the season actually lasts.

City Opening window Closing window Season
Chicago May 28 – Jun 15 Sep 9 – Sep 27 ≈ 105 days
Springfield May 12 – May 31 Sep 9 – Sep 27 ≈ 121 days
Rockford May 21 – Jun 8 Aug 31 – Sep 21 ≈ 106 days

Windows show the stretch when each city's daily average passes through the low-to-mid 60s°F (1991–2020 NOAA records, nearest station to each city). Click a city for its month-by-month table and full season notes.

Season geography

Across Illinois's featured cities, typical openings spread from May 21 to Jun 6, closings from Sep 13 to Sep 19, and the unheated season runs 105–121 days depending on where you are. Elevation, coastal water, and urban heat all pull real dates around, which is exactly why a state-level answer isn't enough.

For your exact town, the pool season lookup takes a ZIP code. Opening day itself is a chemistry job — the dosing calculator turns your first test reading of the year into exact amounts.

Illinois planning pages

When to open — Illinois When to close — Illinois All states →