Case-Fatality Ratio, Population/mi2, Median Household Income, and Unemployment Rate in King County, Washington. A total of 26 zip codes were included. The average CFR was 3.6% and ranged from 2.0% to 9.1%. The population/mi2 ranged from 45.5 to 26,984, with an average of 6,568 population/mi2. Additionally, the average median household income and unemployment rate was $105,633 (Range: $68,994-$188,900) and 3.7% (Range: 2.7%–4.6%), respectively.