Are voter turnout rates declining? The data says no:

Voter turnout rates presented here show that the much-lamented decline in voter participation is an artifact of poor measurement. Previously, turnout rates were calculated by dividing the number of votes by what is called the "voting-age population" which consists of everyone age 18 and older residing in the United States (the yellow line to the right). This includes persons ineligible to vote, mainly non-citizens and ineligible felons, and excludes overseas eligible voters. When turnout rates are calculated for those eligible to vote, a new picture of turnout emerges, which exhibits no decline since 1972 (the green line to the right). Indeed, turnout rates appear to have been restored to their earlier high levels as of 2008.