Counties in Idaho by median age on 1 July (US county estimates)

Adams County had the highest median age on 1 July (US county estimates) of 44 counties in 2018, at 54.5 years. Madison County had the lowest, at 23.1 years. The median was 38.8 years. Source: the U.S. Census Bureau.

Highest54.5Adams County

Lowest23.1Madison County

Median38.844 counties

Map of counties, 2018

Under 34
34 to 36
36 to 39
39 to 44
44 to 49
49 and over

years, 2018. Source: U.S. Census Bureau, Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2018

years. Source: U.S. Census Bureau, Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2018 years	Change on 2017
1	Adams County	54.5	+0.4
2	Boise County	52.8	0
2	Lemhi County	52.8	+0.2
4	Custer County	52.2	-0.7
5	Clearwater County	51	+0.3
5	Idaho County	51	+0.1
7	Lewis County	49.2	+0.9
8	Valley County	49	0
9	Bonner County	48.6	+0.1
10	Shoshone County	47.6	-0.6
11	Benewah County	47.3	+0.4
12	Boundary County	46.4	+1.1
13	Camas County	46.1	-0.5
14	Washington County	45.6	+0.1
15	Gem County	44.4	+0.3
16	Blaine County	44.1	+0.4
17	Butte County	43.3	0
18	Kootenai County	40.9	+0.3
19	Nez Perce County	40.7	+0.3
20	Bear Lake County	40.3	+0.8
21	Oneida County	39.8	-0.3
22	Payette County	39.1	+0.3
23	Owyhee County	38.5	+0.3
24	Clark County	37.4	+0.3
25	Teton County	37.2	+0.7
26	Caribou County	37.1	-0.1
27	Gooding County	36.9	+0.3
28	Ada County	36.8	+0.3
29	Fremont County	36.6	+0.2
30	Minidoka County	35.3	-0.1
31	Lincoln County	35.2	+0.5
31	Twin Falls County	35.2	+0.5
33	Power County	34.5	-0.3
34	Bingham County	34.3	+0.3
35	Bannock County	34	+0.3
36	Canyon County	33.9	+0.3
37	Franklin County	33.8	+0.2
38	Bonneville County	33	+0.2
39	Jerome County	32.9	+0.2
40	Cassia County	32.8	-0.1
41	Elmore County	31.9	-0.2
42	Jefferson County	31.4	-0.2
43	Latah County	30.3	+0.8
44	Madison County	23.1	0

Other periods

About this ranking

Age that divides the resident population of a US county into two halves of equal size on 1 July, from Census Bureau population estimates calculated by single year of age.

Counties only: the county file has no state or national medians, and medians cannot be added up. A single-year estimate, unlike median_age, which for US places is a five-year American Community Survey estimate.

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

U.S. Census Bureau. Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. https://www.census.gov/programs-surveys/popest/data/data-sets.html. 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

U.S. Census Bureau. (2026). Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage (Counties in Idaho by median age on 1 July (US county estimates), 2018) [Data set]. Retrieved October 12, 2026, from https://www.census.gov/programs-surveys/popest/data/data-sets.html

MLA 9

Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage, Counties in Idaho by median age on 1 July (US county estimates), 2018. U.S. Census Bureau, 25 June 2026, https://www.census.gov/programs-surveys/popest/data/data-sets.html. Invokely, https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Census Bureau. 2026. Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. Counties in Idaho by median age on 1 July (US county estimates), 2018. Dataset. Accessed October 12, 2026. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Also distributed by Invokely, https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018.

Harvard

U.S. Census Bureau (2026) Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage, Counties in Idaho by median age on 1 July (US county estimates), 2018 [Dataset]. Available at: https://www.census.gov/programs-surveys/popest/data/data-sets.html, via Invokely: https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2018,
  author = {{U.S. Census Bureau}},
  title = {{Population Estimates Program, county population by age and sex: median age (MEDIAN\_AGE\_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage: Counties in Idaho by median age on 1 July (US county estimates), 2018}},
  year = {2026},
  howpublished = {Data set},
  url = {https://www.census.gov/programs-surveys/popest/data/data-sets.html},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018. Publisher attribution: U.S. Census Bureau. Population Estimates Program, county population by age and sex: median age (MEDIAN\_AGE\_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Retrieved 2026-10-12.},
}

RIS

TY  - DATA
AU  - U.S. Census Bureau
TI  - Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage: Counties in Idaho by median age on 1 July (US county estimates), 2018
PY  - 2026
DA  - 2026/06/25
PB  - U.S. Census Bureau
DB  - Invokely
UR  - https://www.census.gov/programs-surveys/popest/data/data-sets.html
L2  - https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-age-july-1-us-counties/idaho-counties?period=2018.
N1  - Publisher attribution: U.S. Census Bureau. Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Retrieved 2026-10-12.
ER  -

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Questions

Which county has the highest median age on 1 July (US county estimates)?

Adams County, with 54.5 years in 2018, according to the U.S. Census Bureau.

Which county has the lowest median age on 1 July (US county estimates)?

Madison County, with 23.1 years in 2018.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Census Bureau, Population Estimates Program, county population by age and sex: median age (MEDIAN_AGE_TOT) on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage. Retrieved 2026-10-12.