Counties in Illinois by average annual temperature
Massac County had the highest average annual temperature of 102 counties in 2015, at 58.2 °F. Boone County had the lowest, at 48.2 °F. The median was 53.3 °F and the figure for Illinois was 52.9 °F. Source: NOAA National Centers for Environmental Information.
Map of counties, 2015
- Under 50
- 50 to 52
- 52 to 53
- 53 to 54
- 54 to 56
- 56 and over
Top 40 counties, 2015
Full ranking
Other periods
About this ranking
Mean air temperature from January to December, in degrees Fahrenheit: the average of the 12 monthly mean temperatures. NOAA computes it from its climate divisional dataset (nClimDiv): station readings interpolated onto a 5 km grid and averaged over the area.
Values are area averages, so a county with mountains and valleys has one value for very different local climates. NOAA revises the last two years every month.
Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. Equal values share a rank.
How to cite
NOAA National Centers for Environmental Information, Climate at a Glance. NOAA Climate at a Glance, January to December average temperature, counties. From the NOAA Monthly U.S. Climate Divisional Database (nClimDiv), doi:10.7289/V5M32STR. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping. Retrieved 2026-10-12.Citation styles
APA 7
NOAA National Centers for Environmental Information. (2026). NOAA Climate at a Glance, January to December average temperature, counties (Counties in Illinois by average annual temperature, 2015) [Data set]. Retrieved October 12, 2026, from https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping
MLA 9
NOAA Climate at a Glance, January to December average temperature, counties, Counties in Illinois by average annual temperature, 2015. NOAA National Centers for Environmental Information, 6 Oct. 2026, https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping. Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015. Accessed 12 Oct. 2026.
Chicago (author-date)
NOAA National Centers for Environmental Information. 2026. NOAA Climate at a Glance, January to December average temperature, counties. Counties in Illinois by average annual temperature, 2015. Dataset. Accessed October 12, 2026. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping. Also distributed by Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015.
Harvard
NOAA National Centers for Environmental Information (2026) NOAA Climate at a Glance, January to December average temperature, counties, Counties in Illinois by average annual temperature, 2015 [Dataset]. Available at: https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping, via Invokely: https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015 (Accessed: 12 October 2026).
BibTeX
@misc{noaa_counties_in_illinois_by_2015,
author = {{NOAA National Centers for Environmental Information}},
title = {{NOAA Climate at a Glance, January to December average temperature, counties: Counties in Illinois by average annual temperature, 2015}},
year = {2026},
howpublished = {Data set},
url = {https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping},
urldate = {2026-10-12},
note = {Accessed via Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015. Publisher attribution: NOAA National Centers for Environmental Information, Climate at a Glance. NOAA Climate at a Glance, January to December average temperature, counties. From the NOAA Monthly U.S. Climate Divisional Database (nClimDiv), doi:10.7289/V5M32STR. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping. Retrieved 2026-10-12.},
}
RIS
TY - DATA
AU - NOAA National Centers for Environmental Information
TI - NOAA Climate at a Glance, January to December average temperature, counties: Counties in Illinois by average annual temperature, 2015
PY - 2026
DA - 2026/10/06
PB - NOAA National Centers for Environmental Information
DB - Invokely
UR - https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping
L2 - https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015
Y2 - 2026/10/12
N1 - Accessed via Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2015.
N1 - Publisher attribution: NOAA National Centers for Environmental Information, Climate at a Glance. NOAA Climate at a Glance, January to December average temperature, counties. From the NOAA Monthly U.S. Climate Divisional Database (nClimDiv), doi:10.7289/V5M32STR. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/mapping. Retrieved 2026-10-12.
ER -
Use this data in your AI agent
Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:
Rank Counties in Illinois by average annual temperature using official data, and cite the source.
rank_places {"indicator":"average_temperature_annual","level":"province","within":"Illinois","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=average_temperature_annual&level=province&within=Illinois&limit=10Questions
Which county has the highest average annual temperature?
Massac County, with 58.2 °F in 2015, according to NOAA National Centers for Environmental Information.
Which county has the lowest average annual temperature?
Boone County, with 48.2 °F in 2015.
Where does this ranking come from?
Every value comes from one source and one period, so the places are comparable: NOAA National Centers for Environmental Information, NOAA Climate at a Glance, January to December average temperature, counties. Retrieved 2026-10-12.
Average annual temperature: other rankings
Counties in Illinois: more rankings
- Share of days unhealthy for sensitive groups or worse (US EPA AQI)
- Expected annual loss from natural hazards (FEMA National Risk Index)
- Highest daily Air Quality Index (US EPA)
- Median Air Quality Index (US EPA)
- Real GDP growth
- GDP per capita, US dollars
- Gross domestic product (GDP), US dollars
- Median age on 1 July (US county estimates)