From the U.S. Census:
The U.S. Census Bureau released today selected characteristics of the citizen voting-age population from the 2015 American Community Survey.
[Data tables] present estimates of the citizen, 18 and older population for all states and congressional districts. Selected characteristics include age, sex, race, Hispanic Origin, educational attainment, poverty status, and household income.
Direct to Electorate Profiles: Selected Characteristics of the Citizen, 18 and Older Population