Mercer Island, Washington's estimated population is 25,976 according to the most recent United States census estimates. Mercer Island, Washington is the 42nd largest city in Washington based on official 2017 estimates from the US Census Bureau.
The population density is 4074.08 people/mi² (1573.00 people/km²).
The overall median age is 45.5 years, 45.4 years for males, and 45.5 years for females. For every 100 females there are 93.1 males.
Based on data from the American Community Survey, in 2017 there were households in the city, with an average size of 2.5 people per household. The homeowner vacancy rate was %, with a median rent of $/month. The median house has rooms, and has a value of $.
The median income for households in Mercer Island, Washington is $136,644, while the mean household income is $206,003.
According to the most recent ACS, the racial composition of Mercer Island Wa was:
| Year | Population | Growth | Annual Growth Rate |
| 2018 | 25,976 | 223 | 0.87% |
| 2017 | 25,753 | 135 | 0.53% |
| 2016 | 25,618 | 237 | 0.93% |
| 2015 | 25,381 | 621 | 2.51% |
| 2014 | 24,760 | 317 | 1.30% |
| 2013 | 24,443 | 385 | 1.60% |
| 2012 | 24,058 | 516 | 2.19% |
| 2011 | 23,542 | 773 | 3.39% |
| 2010 | 22,769 | 733 | 0.33% |
| 2000 | 22,036 | 1,220 | 0.57% |
| 1990 | 20,816 | -706 | -0.33% |
| 1980 | 21,522 | 2,475 | 1.23% |
| 1970 | 19,047 | 7,047 | 4.73% |
| 1960 | 12,000 | 0.00% |
| Race | Population |
| White | 18,554 |
| Asian | 4,683 |
| Two or More Races | 907 |
| Black or African American | 447 |
| Some Other Race | 152 |
| Native Hawaiian and Other Pacific Islander | 17 |
| American Indian and Alaska Native | 8 |
45.5
45.4
45.5
There are 18,847 adults, (4,912 of whom are seniors) in Mercer Island Wa.
Female
12,826
51.78%
Male
11,942
48.22%
| Type | Count | Average Size | Owned |
| All | 9,867 | 2.5 | 70.4 |
| Married | 6,079 | 3.07 | 85.6 |
| Non Family | 2,838 | 1.21 | 41.8 |
| Female | 601 | 2.79 | 68.1 |
| Male | 349 | 2.58 | 44.1 |
| Education Attained | Count | Percentage |
| Less Than 9th Grade | 125 | 0.71% |
| 9th to 12th Grade | 247 | 1.41% |
| High School Graduate | 903 | 5.14% |
| Some College | 1,786 | 10.16% |
| Associates Degree | 779 | 4.43% |
| Bachelors Degree | 7,296 | 41.51% |
| Graduate Degree | 6,441 | 36.64% |
| Name | Total | High School | Bachelors |
| White | 13,095 | 12,930 | 10,426 |
| Asian | 3,308 | 3,136 | 2,579 |
| Hispanic | 454 | 442 | 247 |
| Multiple Races | 406 | 403 | 257 |
| Black | 301 | 281 | 200 |
| Other Race | 82 | 75 | 52 |
| Native American | 8 | 8 | 7 |
The highest rate of high school graduation is among native american people with a rate of 100.00%.
The highest rate of bachelors degrees is among native american people with a rate of 87.50%.
$85,270
Average Earnings
$118,500
Average Male
$52,772
Average Female
82.44% of Mercer Island Wa residents speak only English, while 17.56% speak other languages. The non-English language spoken by the largest group is Asian and Pacific Island languages, which is spoken by 9.08% of the population.
| Name | Total | In Poverty | Poverty Rate |
| White | 17,809 | 695 | 3.90% |
| Asian | 4,664 | 217 | 4.65% |
| Black | 447 | 66 | 14.77% |
| Hispanic | 718 | 52 | 7.24% |
| Multiple | 899 | 21 | 2.34% |
| Islander | 17 | 17 | 100.00% |
| Other | 145 | 1 | 0.69% |
4.34%
Overall Poverty Rate
2.97%
Male Poverty Rate
5.61%
Female Poverty Rate
The race most likely to be in poverty in Mercer Island Wa is Islander, with 100.00% below the poverty level.
The race least likely to be in poverty in Mercer Island Wa is Other, with 0.69% below the poverty level.
The poverty rate among those that worked full-time for the past 12 months was 0.70%. Among those working part-time, it was 8.11%, and for those that did not work, the poverty rate was 6.94%.
63.9%
Overall Marriage Rate
67.6%
Male Marriage Rate
60.5%
Female Marriage Rate
The age group where males are most likely to be married is 35-44, while the female age group most likely to be married is 35-44.
| Name | Veterans | % of Total |
| White | 1,330 | 9.24% |
| Asian | 118 | 3.38% |
| Black | 54 | 15.38% |
| 2 or More | 43 | 8.67% |
| Hispanic | 12 | 2.45% |
| Other | 12 | 13.33% |
2.08%
Veteran Poverty Rate
31.54%
Veteran Disability Rate
61.5%
Labor Force Participation
58.9%
Employment Rate
4.2%
Unemployment Rate
Non citizens include legal permanent residents (green card holders), international students, temporary workers, humanitarian migrants, and illegal immigrants.
81.48%
Native Born
18.52%
Foreign Born
6.15%
Non Citizen
81.48% of Mercer Island Wa residents were born in the United States, with 37.67% having been born in Washington. 6.15% of residents are not US citizens. Of those not born in the United States, the largest percentage are from Asia.