Romeoville (IL) Temperature by Month
The average annual maximum temperature in Romeoville, Illinois, United States of America is 15°C (59°F), with daytime highs ranging from 0°C (32°F) in January to 29°C (84°F) in July. This page covers monthly averages, day-night differences, and how Romeoville compares to cities worldwide.
Romeoville Monthly Temperatures
In Romeoville, temperatures differ significantly between summer and winter months. Nighttime lows reflect this range, dropping from 18°C (64°F) in July to -9°C (16°F) in January.
The chart below illustrates the average maximum day and minimum night temperatures in Romeoville by month:
Low temperatures are most often recorded between 4 AM and 6 AM, while highs typically occur around 3 PM. July, the city's warmest month, sees 319 hours of sunshine.
The chart below shows the average temperature throughout the year:
Temperature: Romeoville vs the United States of America
The map below shows the annual temperature across the United States of America. You can also select individual months if you want to compare a specific time of year.
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Romeoville vs World: Temperature Compared
Romeoville's average annual maximum temperature is 15°C (59°F). To put that in context, here's how it compares to a few well-known destinations:
Barcelona, Spain has an annual average of around 21°C (70°F), with warm summers and mild, fairly short winters.
Queenstown, New Zealand averages 10°C (50°F) annually — remember seasons are flipped, so its coldest months fall in June and July.
New York City, USA averages 17°C (63°F) a year, with hot humid summers and cold winters that bring regular snowfall.
Perth, Australia averages 25°C (77°F) annually, with a classic Mediterranean climate — hot dry summers and mild wet winters.
What Does the Temperature Feel Like in Romeoville?
Temperature alone doesn't tell the whole story — humidity plays a big role in how warm or cold it actually feels. High humidity in summer makes the heat feel more intense, particularly once temperatures climb above 25°C. In winter, the same humidity can make cold air feel sharper than the thermometer suggests.
In the cooler months, when temperatures drop below 10°C, high humidity makes the cold feel more cutting than it would in dry conditions.
In Romeoville, January is the coolest month, with average highs of 0°C (32°F) and humidity around 72% — considered high. In July, the warmest month, temperatures average 29°C (84°F) with 68% humidity — conditions that feel high. For a full picture, see our humidity page.
Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.
The readings come from a range of sources — land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.
Global average temperatures have risen by around 1.2°C since the pre-industrial era, and the effects are visible across many regions. Winters are milder on average, with fewer frost days and less snow in many parts of the world. Heatwaves are more frequent and more intense, and Europe's summers of 2018, 2019, and 2020 all set records.
Summers are also getting drier in some areas, while winter rainfall has increased in others. This contributies to higher river levels and more flooding. In many countries, spring arrives earlier and autumn lasts longer. It has knock-on effects for wildlife, agriculture, and local ecosystems.
For more on Romeoville's weather — including monthly rainfall, sunshine hours, and humidity — visit our Romeoville climate page.
