Counties in Illinois by average annual temperature

Alexander County had the highest average annual temperature of 102 counties in 2018, at 58 °F. Boone County had the lowest, at 47.4 °F. The median was 52.9 °F and the figure for Illinois was 52.5 °F. Source: NOAA National Centers for Environmental Information.

Highest58Alexander County

Lowest47.4Boone County

Median52.9102 counties

Illinois52.5History

Top 40 counties, 2018

°F. Source: NOAA NCEI, NOAA Climate at a Glance, January to December average temperature, counties. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2018 °F	Change on 2017
1	Alexander County	58	-2%
1	Pulaski County	58	-2.2%
3	Massac County	57.9	-2.7%
4	Hardin County	56.9	-3.1%
4	Monroe County	56.9	-3.6%
4	Pope County	56.9	-3.1%
4	Union County	56.9	-2.4%
8	Johnson County	56.8	-2.7%
9	Gallatin County	56.6	-3.2%
10	St. Clair County	56.5	-3.7%
11	Randolph County	56.3	-3.4%
11	Saline County	56.3	-3.4%
11	White County	56.3	-3.8%
14	Edwards County	56.2	-3.3%
14	Jackson County	56.2	-2.8%
14	Wabash County	56.2	-2.4%
14	Williamson County	56.2	-2.8%
18	Franklin County	56.1	-2.9%
18	Hamilton County	56.1	-3.9%
20	Wayne County	55.9	-4%
21	Perry County	55.8	-3.1%
22	Clinton County	55.7	-3.3%
22	Lawrence County	55.7	-1.9%
24	Jefferson County	55.5	-3.3%
24	Madison County	55.5	-3.5%
24	Washington County	55.5	-3.5%
27	Richland County	55.4	-2.6%
28	Clay County	55	-3.2%
29	Crawford County	54.9	-2.3%
29	Jersey County	54.9	-3%
29	Marion County	54.9	-3.3%
32	Bond County	54.8	-3.5%
33	Calhoun County	54.7	-3%
34	Jasper County	54.6	-2.5%
35	Greene County	54.3	-3%
36	Fayette County	54.2	-3.6%
37	Pike County	54.1	-3.2%
38	Effingham County	54	-3.4%
39	Clark County	53.9	-3.1%
39	Cumberland County	53.9	-3.2%
39	Macoupin County	53.9	-3.4%
39	Scott County	53.9	-3.2%
43	Montgomery County	53.6	-3.8%
44	Brown County	53.3	-3.1%
44	Christian County	53.3	-3.6%
44	Coles County	53.3	-3.6%
44	Shelby County	53.3	-3.8%
48	Adams County	53.1	-3.5%
48	Morgan County	53.1	-3.8%
48	Sangamon County	53.1	-4%
51	Douglas County	52.9	-3.8%
51	Moultrie County	52.9	-3.6%
53	Cass County	52.8	-4%
54	Mason County	52.7	-3.8%
54	Menard County	52.7	-4.2%
54	Schuyler County	52.7	-3.3%
57	Edgar County	52.6	-3.8%
57	Macon County	52.6	-3.7%
59	Logan County	52.5	-3.7%
60	Piatt County	52.3	-3.9%
60	Tazewell County	52.3	-3.5%
62	Champaign County	52.1	-3.9%
62	Hancock County	52.1	-3.7%
64	De Witt County	52	-3.7%
65	Fulton County	51.9	-3.5%
65	Vermilion County	51.9	-3.5%
67	McDonough County	51.6	-3.6%
67	Peoria County	51.6	-3.7%
69	Woodford County	51.3	-3.8%
70	Ford County	51.2	-3.8%
70	Iroquois County	51.2	-3.2%
70	McLean County	51.2	-4.1%
73	Henderson County	50.9	-4.1%
74	Kankakee County	50.7	-3.2%
75	Marshall County	50.6	-3.6%
76	Grundy County	50.4	-3.3%
77	Livingston County	50.2	-4.6%
77	Warren County	50.2	-3.8%
79	Knox County	50.1	-3.8%
79	Putnam County	50.1	-3.3%
79	Will County	50.1	-3.5%
82	Cook County	50	-3.3%
82	Mercer County	50	-4%
84	Rock Island County	49.9	-3.9%
84	Stark County	49.9	-4%
86	LaSalle County	49.8	-3.3%
87	DuPage County	49.6	-2.9%
87	Henry County	49.6	-4.1%
87	Kendall County	49.6	-3.3%
90	Bureau County	49.3	-3.3%
91	Whiteside County	49.2	-4.3%
92	Lee County	48.8	-3.9%
93	Kane County	48.6	-3.4%
94	Lake County	48.5	-3.2%
95	Carroll County	48.4	-4.2%
95	Ogle County	48.4	-4%
97	DeKalb County	48.3	-3.6%
98	McHenry County	47.7	-3.8%
98	Stephenson County	47.7	-4%
98	Winnebago County	47.7	-4.8%
101	Jo Daviess County	47.6	-3.8%
102	Boone County	47.4	-4.4%

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

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

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, 2018) [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, 2018. 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=2018. 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, 2018. 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=2018.

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, 2018 [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=2018 (Accessed: 12 October 2026).

BibTeX

@misc{noaa_counties_in_illinois_by_2018,
  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, 2018}},
  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=2018. 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, 2018
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=2018
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties?period=2018.
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  -

Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Embed code

<iframe src="https://invokely.ai/embed/rankings/average-annual-temperature/illinois-counties?period=2018" width="760" height="500" title="Counties in Illinois by average annual temperature, 2018, chart from Invokely" loading="lazy" style="border:0;width:100%;max-width:760px" referrerpolicy="strict-origin-when-cross-origin"></iframe>

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

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=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

Which county has the highest average annual temperature?

Alexander County, with 58 °F in 2018, according to NOAA National Centers for Environmental Information.

Which county has the lowest average annual temperature?

Boone County, with 47.4 °F in 2018.

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.