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Mercer Island’s population changed very little (just 3%) from 2000 to 2010, but the number of households grew by 15%. This implies smaller households, which is reflected in the City’s household types. A majority of Mercer Island households (61%) consist of only one or two persons. This compares to 58% in 2000 and 49% in 1980, and is consistent with overall smaller households in most parts of the County.

What differentiates Mercer Island from other East King County (EKC) cities (aside from the Point Cities) is the relatively high percentage of married couples without children—35% of all households. As in other “maturing suburbs” (typically incorporated before 1990, little or no annexation), the City has many empty nesters who continue to live where they raised their families. And unlike most of the rest of East King County, Mercer Island experienced an actual small decline in married couples with children.

Mercer Island has a larger proportion of school-age children and senior adults and lower percentages of younger (age 20 to 44) adults. Note that, according to the Mercer Island School District, more than 100 students now live in the Town Center, a demographic believed to be rising. In addition, the 34-to-44 age group fell in proportion, while the 55-to-64 age group rose.

Simply stated, Mercer Island households were older and smaller in 2010 than they were 30 years before, and that trend is not expected to change. Mercer Island’s challenge is to provide a variety of housing opportunities in a community that has limited capacity for new development and does not anticipate or desire any significant changes to its existing residential areas.

Several policies are outlined in subsequent sections of the housing element to address these changing needs. These include encouraging the continued use of accessory dwelling units, providing opportunities for senior housing, and enabling innovative forms of single family housing. These forms of housing, both rental and ownership, may provide some alternatives for smaller households, including households looking to downsize from single family homes. An accessory unit built into an existing home can provide a separate living unit that provides additional income to the home owner as well as more affordable living or variety in lifestyle choice for renters.