Decatur weather in May 2026

Q: How hot is it in Decatur in May?

Daytime temperatures usually reach 21°C in Decatur in May, falling to 9°C at night.

Q: How sunny is it in Decatur in May?

There are normally 9 hours of bright sunshine each day in Decatur in May - that's 62% of daylight hours.

Q: Is the sea cold around Decatur in May?

The average sea temperature around Decatur in May is 6°C.

Q: Does it rain in Decatur in May?

There are usually 11 days with some rain in Decatur in May and the average monthly rainfall is 84mm.

Expect daytime maximum temperatures of 75°F in Decatur, Illinois in May based on long-term weather averages. There are 9 hours of sunshine per day on average with 10 days with some rainfall and typically 4.0 inches of rainfall in the month.

75
75°F max day temperature
9
9 hours of sunshine per day
10
10 days with some rainfall
52
52°F min night temperature
14
14 hours of daylight per day
0
No heat & humidity
4.0
4.0 inches of monthly rainfall
8
8 (Very High) UV index

More about Decatur

Decatur by month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Recommended for Illinois

Air Canada: Top flight deals to the USA

Sale

Discover top Air Canada offers on flights to the USA
Browse lowest fares available or search by date
Book flights to New York, Orlando, LA, Boston & more

Go to Air Canada deal >>

View all Air Canada offers

The May weather guide for Illinois (Decatur) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C) | Imperial (°F)