Ada County, ID population age distribution
A complete breakdown of Ada County's age demographics from 0 to 85 years, distributed across 18 age groups is listed in the table below.
Age Group | Population | % of Total Population |
---|---|---|
Under 5 years | 26,705 | 5.5% |
5 to 9 years | 29,030 | 5.98% |
10 to 14 years | 36,880 | 7.6% |
15 to 19 years | 33,255 | 6.85% |
20 to 24 years | 28,747 | 5.92% |
25 to 29 years | 33,625 | 6.93% |
30 to 34 years | 34,648 | 7.14% |
35 to 39 years | 37,403 | 7.71% |
40 to 44 years | 32,509 | 6.7% |
45 to 49 years | 32,147 | 6.62% |
50 to 54 years | 30,258 | 6.24% |
55 to 59 years | 31,646 | 6.52% |
60 to 64 years | 27,218 | 5.61% |
65 to 69 years | 25,478 | 5.25% |
70 to 74 years | 19,377 | 3.99% |
75 to 79 years | 12,177 | 2.51% |
80 to 84 years | 7,494 | 1.54% |
85 years and over | 6,649 | 1.37% |
TABLE OF CONTENTS
Ada County, ID population by age group
Sources: U.S. Census Bureau, American Community Survey (ACS) 2021

The largest age group in Ada County, ID was for the group of age 35-39 years with a population of 37,403 (7.71%), according to the 2021 American Community Survey.
At the same time, the smallest age group in Ada County, ID was the 85+ years with a population of 6,649 (1.37%).
Ada County, ID population by age cohort
To better understand the age distribution of Ada County, ID's population, we divided it into the following 3 cohorts:
- Children : Under the age of 18 years
- Adults (working population): Between the age of 18 and 64 years
- Seniors: 65 years and above

Here's the population for each of the three cohorts.
Age Group | Population | % of Total Population |
---|---|---|
Under 18 years | 113,471 | 23.38% |
18 to 64 years | 300,600 | 61.95% |
85 years and over | 71,175 | 14.67% |
Key stats for each age cohort as per our analysis of U.S. Census Bureau American Community Survey:
- Ada County's population under 18 was 23.38%, compared to the 22.51% nationwide.
- Ada County's working population (between 18 and 64) was 61.95%, compared to 61.45% nationwide.
- Ada County's elderly or the senior population (over 65 age) was 14.67% as compared to 16.04% nationwide.
Ada County, ID population pyramid
Population pyramid for Ada County, ID is charted below using the estimates from U.S. Census Bureau's American Community Survey 5-Year estimates. A wide base suggests population increase, narrow base indicates declining birth rates.
Key stats from our analysis of the Ada County's population pyramid:
- Youth dependency ratio, which is the number of children aged 0-14 per 100 persons aged 15-64, for Ada County, ID, is 28.8.
- Old-age dependency ratio, which is the number of persons aged 65 or over per 100 persons aged 15-64, for Ada County, ID, is 22.1.
- Total dependency ratio for Ada County, ID is 51.0.
- Potential support ratio, which is the number of youth (working age population) per elderly, for Ada County, ID is 4.5.

Here's the Ada County, ID's male and female population across different age groups:
Age Group | Population(Male) | Population(Female) | Total Population |
---|---|---|---|
Under 5 years | 13,637 | 13,068 | 26,705 |
5 to 9 years | 14,840 | 14,190 | 29,030 |
10 to 14 years | 18,853 | 18,027 | 36,880 |
15 to 19 years | 17,120 | 16,135 | 33,255 |
20 to 24 years | 14,919 | 13,828 | 28,747 |
25 to 29 years | 17,427 | 16,198 | 33,625 |
30 to 34 years | 17,487 | 17,161 | 34,648 |
35 to 39 years | 18,813 | 18,590 | 37,403 |
40 to 44 years | 16,934 | 15,575 | 32,509 |
45 to 49 years | 16,744 | 15,403 | 32,147 |
50 to 54 years | 15,482 | 14,776 | 30,258 |
55 to 59 years | 15,881 | 15,765 | 31,646 |
60 to 64 years | 13,042 | 14,176 | 27,218 |
65 to 69 years | 12,180 | 13,298 | 25,478 |
70 to 74 years | 9,288 | 10,089 | 19,377 |
75 to 79 years | 5,605 | 6,572 | 12,177 |
80 to 84 years | 3,473 | 4,021 | 7,494 |
85 years and over | 2,377 | 4,272 | 6,649 |
Things to know
What is the population of Ada County, ID under 18?
Ada County's population under the age of 18 is 113,471, as per the latest U.S. Census Bureau's American Community Survey estimates. This population is 23.38% of the total resident population of Ada County, ID.
What is the aging population in Ada County, ID?
Ada County's population aged 65 years and above was 71,175. As per the U.S. Census Bureau's American Community Survey, this population is 14.67% of the entire population.
References
- U.S. Census Bureau American Community Survey (ACS) 2017-2021 5-Year Estimates