Counties in Illinois by average annual temperature, 2025

Alexander County had the highest average annual temperature of 102 counties in 2025, at 58.7 °F. Stephenson County had the lowest, at 48.8 °F. The median was 53.8 °F and the figure for Illinois was 53.6 °F. Source: NOAA National Centers for Environmental Information.

Highest58.7Alexander County

Lowest48.8Stephenson County

Median53.8102 counties

Illinois53.6History

Top 40 counties, 2025

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

Full ranking

Rank	Counties	2025 °F	Change on 2024
1	Alexander County	58.7	-2.7%
1	Pulaski County	58.7	-2.8%
3	Massac County	58.6	-3%
4	Hardin County	57.8	-2.4%
5	Pope County	57.7	-2.7%
6	Gallatin County	57.4	-3%
6	Johnson County	57.4	-2.9%
8	Union County	57.3	-2.9%
9	Monroe County	57.2	-2.9%
9	White County	57.2	-3.4%
11	Franklin County	57.1	-3.2%
11	Jackson County	57.1	-3.2%
11	Perry County	57.1	-3.2%
11	Saline County	57.1	-2.7%
15	Jefferson County	57	-2.4%
15	Williamson County	57	-2.9%
17	Hamilton County	56.9	-3.1%
17	Randolph County	56.9	-2.6%
17	St. Clair County	56.9	-2.4%
17	Wabash County	56.9	-2.6%
21	Edwards County	56.8	-2.7%
21	Washington County	56.8	-2.6%
23	Clinton County	56.6	-2.6%
23	Wayne County	56.6	-2.6%
25	Marion County	56.2	-2.8%
26	Lawrence County	56.1	-2.6%
26	Richland County	56.1	-2.6%
28	Clay County	56	-2.8%
28	Madison County	56	-3.4%
30	Jersey County	55.8	-3%
31	Bond County	55.7	-3.3%
31	Calhoun County	55.7	-2.5%
33	Crawford County	55.6	-3%
33	Jasper County	55.6	-3%
35	Fayette County	55.4	-3%
36	Effingham County	55.2	-2.8%
37	Greene County	55.1	-2.7%
38	Clark County	54.8	-3.5%
38	Cumberland County	54.8	-3.2%
40	Macoupin County	54.7	-3.5%
40	Pike County	54.7	-2.5%
42	Montgomery County	54.6	-3.7%
42	Scott County	54.6	-2.5%
44	Shelby County	54.3	-2.9%
45	Coles County	54.2	-3%
46	Adams County	54.1	-3.2%
46	Christian County	54.1	-3.6%
46	Morgan County	54.1	-2.9%
49	Cass County	53.9	-2.9%
49	Douglas County	53.9	-3.1%
51	Brown County	53.8	-3.1%
51	Moultrie County	53.8	-2.9%
53	Edgar County	53.7	-3.4%
54	Mason County	53.6	-3.6%
54	Sangamon County	53.6	-3.8%
56	Schuyler County	53.5	-3.3%
57	Fulton County	53.4	-3.4%
57	Macon County	53.4	-3.1%
57	Piatt County	53.4	-3.1%
57	Tazewell County	53.4	-3.3%
61	Champaign County	53.2	-3.1%
61	Hancock County	53.2	-3.1%
61	Menard County	53.2	-3.6%
61	Peoria County	53.2	-3.6%
65	Logan County	53.1	-3.5%
66	De Witt County	53	-3.1%
67	McLean County	52.8	-2.9%
68	McDonough County	52.7	-3.3%
68	Woodford County	52.7	-3.1%
70	Henderson County	52.6	-2.8%
70	Vermilion County	52.6	-3.5%
72	Marshall County	52.3	-3.7%
73	Ford County	52.2	-3.7%
73	Knox County	52.2	-3.2%
73	Livingston County	52.2	-3.7%
73	Warren County	52.2	-3%
77	Mercer County	52.1	-3.2%
77	Stark County	52.1	-3.5%
79	Iroquois County	51.7	-4.1%
79	Putnam County	51.7	-4.1%
79	Rock Island County	51.7	-3.7%
82	Grundy County	51.6	-4.4%
82	Henry County	51.6	-3.6%
84	Kankakee County	51.5	-4.1%
85	Bureau County	51.3	-3.8%
85	Will County	51.3	-4.3%
87	Cook County	51.2	-5.2%
87	Whiteside County	51.2	-3.8%
89	Kendall County	51.1	-4.3%
90	LaSalle County	51	-4.3%
91	DuPage County	50.9	-4.9%
92	Lee County	50.6	-4%
93	Kane County	50.3	-4.4%
94	DeKalb County	50	-4.4%
94	Lake County	50	-5.1%
96	Carroll County	49.9	-4.2%
96	Ogle County	49.9	-4.4%
98	Winnebago County	49.6	-5%
99	Boone County	49.4	-5%
100	McHenry County	49.1	-5%
101	Jo Daviess County	49	-4.3%
102	Stephenson County	48.8	-4.7%

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, 2025) [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, 2025. 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. 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, 2025. 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.

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, 2025 [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 (Accessed: 12 October 2026).

BibTeX

@misc{noaa_counties_in_illinois_by_2025,
  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, 2025}},
  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. 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, 2025
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
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/average-annual-temperature/illinois-counties.
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  -

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Questions

Which county has the highest average annual temperature?

Alexander County, with 58.7 °F in 2025, according to NOAA National Centers for Environmental Information.

Which county has the lowest average annual temperature?

Stephenson County, with 48.8 °F in 2025.

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.