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2025 Demographics

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Age Data for County: San Mateo

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Population by Age Group County: San Mateo State: California
Persons % of Population Persons % of Population
0-4 35,722 4.89% 2,093,815 5.39%
5-9 37,365 5.11% 2,224,077 5.72%
10-14 39,359 5.39% 2,393,042 6.16%
15-17 24,142 3.30% 1,467,805 3.78%
18-20 24,581 3.36% 1,628,036 4.19%
21-24 31,887 4.36% 2,072,236 5.33%
25-34 93,684 12.82% 5,476,161 14.09%
35-44 107,977 14.78% 5,470,158 14.07%
45-54 98,419 13.47% 4,850,608 12.48%
55-64 95,523 13.07% 4,646,903 11.95%
65-74 77,790 10.65% 3,744,000 9.63%
75-84 45,111 6.17% 2,046,221 5.26%
85+ 19,130 2.62% 757,420 1.95%
Population by Age
Population by Age County: San Mateo State: California
Persons % of Population Persons % of Population
Under 18 136,588 18.69% 8,178,739 21.04%
18+ 594,102 81.31% 30,691,743 78.96%
25+ 537,634 73.58% 26,991,471 69.44%
65+ 142,031 19.44% 6,547,641 16.84%
85+ 19,130 2.62% 757,420 1.95%
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Median Age by Sex County: San Mateo State: California
Years Years
All 42.3 38.8
Male 41.1 37.9
Female 43.5 39.8
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Male Population by Age Group County: San Mateo State: California
Persons % of Male Population Persons % of Male Population
0 - 4 18,213 5.00% 1,070,051 5.50%
5 - 9 19,137 5.25% 1,138,168 5.85%
10 - 14 20,261 5.56% 1,226,038 6.31%
15 - 17 12,458 3.42% 752,976 3.87%
18 - 20 12,677 3.48% 832,326 4.28%
21 - 24 16,518 4.54% 1,069,925 5.50%
25 - 34 48,952 13.44% 2,827,595 14.54%
35 - 44 55,523 15.25% 2,806,612 14.43%
45 - 54 49,639 13.63% 2,452,777 12.62%
55 - 64 47,289 12.98% 2,314,115 11.90%
65 - 74 36,988 10.16% 1,774,103 9.12%
75 - 84 19,668 5.40% 901,973 4.64%
85+ 6,874 1.89% 276,514 1.42%
Male Population by Age
Male Population by Age County: San Mateo State: California
Persons % of Male Population Persons % of Male Population
Under 18 70,069 19.24% 4,187,233 21.54%
18+ 294,128 80.76% 15,255,940 78.46%
65+ 63,530 17.44% 2,952,590 15.19%
85+ 6,874 1.89% 276,514 1.42%
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Female Population by Age Group County: San Mateo State: California
Persons % of Female Population Persons % of Female Population
0 - 4 17,509 4.78% 1,023,764 5.27%
5 - 9 18,228 4.97% 1,085,909 5.59%
10 - 14 19,098 5.21% 1,167,004 6.01%
15 - 17 11,684 3.19% 714,829 3.68%
18 - 20 11,904 3.25% 795,710 4.10%
21 - 24 15,369 4.19% 1,002,311 5.16%
25 - 34 44,732 12.21% 2,648,566 13.63%
35 - 44 52,454 14.31% 2,663,546 13.71%
45 - 54 48,780 13.31% 2,397,831 12.34%
55 - 64 48,234 13.16% 2,332,788 12.01%
65 - 74 40,802 11.13% 1,969,897 10.14%
75 - 84 25,443 6.94% 1,144,248 5.89%
85+ 12,256 3.34% 480,906 2.48%
Female Population by Age
Female Population by Age County: San Mateo State: California
Persons % of Female Population Persons % of Female Population
Under 18 66,519 18.15% 3,991,506 20.55%
18+ 299,974 81.85% 15,435,803 79.45%
65+ 78,501 21.42% 3,595,051 18.51%
85+ 12,256 3.34% 480,906 2.48%
Demographics information provided by Claritas, updated May 2025, under these terms of use.