Pool season · Illinois
Round Lake Beach Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Round Lake Beach'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.
Round Lake Beach, IL — 65 swim days a yearEach dot on the bar is one week of Round Lake Beach's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (May 4–May 25), solid teal is swim season, and hollow amber is the closing window ending October 2. The black marker is today — its position against the colors is the entire executive summary.
The Round Lake Beach pool calendar
Opening — target May 11
Target May 11; the practical window runs May 4–May 25, and the 7-day mean crosses the 61°F threshold around May 25. Cold-water starts are the cheap ones.
Closing — deadline October 2
The window opens September 22 once water leaves the algae zone; the model deadline is October 2, a week ahead of the October 23 freeze normal.
Estimated water temperature by month
This is Round Lake Beach'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 24° | 23° | 31° | 42° | 53° | 64° | 72° | 72° | 68° | 58° | 45° | 33° |
The curve peaks near 73°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Rockford's pool season and Schaumburg's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Illinois season index.
Round Lake Beach pool season FAQ
When should I open my pool in Round Lake Beach, IL?
Target May 11. That date backs off two weeks from the day Round Lake Beach's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Round Lake Beach opening guide.
When should I close my pool in Round Lake Beach?
The closing deadline is October 2 — late enough that the water has cooled out of the algae zone, early enough to beat Round Lake Beach's first-freeze normal by about a week. See the Round Lake Beach closing guide for the winterizing steps.
How long is the swim season in Round Lake Beach?
Round Lake Beach averages 65 days a year with normal highs of 80°F or better — about 6 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 Round Lake Beach?
An unheated pool near Round Lake Beach typically peaks around 73°F in high summer and bottoms out near 22°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 Round Lake Beach hits the closing window
Data: NOAA 1991–2020 climate normals via Lake Villa 2ne (3.7 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.