"Maine and Vermont remain the only states that allow prison inmates to vote. Thirty U.S. states deny voting rights to felony probationers, and thirty-five states disenfranchise parolees. In the most extreme cases, eleven states continue to deny voting rights to some or all of the “ex-felons” who have successfully fulfilled their prison, parole, or probation sentences"

Source

Christopher Uggen, Sarah Shannon, and Jeff Manza, "State-Level Estimates of Felon Disenfranchisement in the United States, 2010" (Washington, DC: The Sentencing Project, July 2012), p. 2.
http://sentencingproject.org/…