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The median age in Washington County is above both the U.S. median age of 37.6 years and the state’s 38.1 years. According to the 2015 American Community Survey, Washington County’s median age was 41.5 years old. That’s an increase of 2.7 years from the 2000 census. However, while there’s an overall increase from 2000, there’s a slight decrease from the median age of 41.6 years in the 2010 census. Area counties were at similar rates as Washington County in 2015 with Iowa County at 42.4, Keokuk at 44.3, Jefferson at 42.5, Louisa at 40.8, and Henry at 41.5. Johnson County was the second lowest in the state at 29.8 years old.

County – 2015, 2010, 2000 (change since 2000)
Henry – 40.7, 40.2, 37.1 (+3.6)
Iowa – 42.4, 42.4, 38.8 (+3.6)
Jefferson – 42.5, 43.5, 41.1 (+1.4)
Johnson – 29.8, 29.3, 28.4 (+1.4)
Keokuk – 44.3, 43.8, 40.0 (+4.3)
Louisa – 40.8, 39.8, 35.9 (+4.9)
Washington – 41.5, 41.6, 38.8 (+2.7)