Read: Polls for prisons

The exact number of people in American jails who are legally permitted to vote is unknown, but it’s safe to say that Massey is far from alone. Chris Uggen, a sociology professor at the University of Minnesota who has studied what he refers to as “practical disenfranchisement,” posits that “a good portion” of the U.S. jail population, which hovers at around 600,000 people, retains the right. Jail populations fluctuate constantly, which makes pinning down an estimate of the voting population inside especially difficult.

Similarly, it’s hard to know what portion of those eligible voters are not voting because they are unaware of their rights or because their rights are being denied. The 1974 Supreme Court decision O’Brien v. Skinner protects the right of certain inmates to vote in elections without interference from government. But the Court left it up to state and local jurisdictions to decide how exactly to comply with the law.

“There is no national organization that is the anchoring institution to ensure that residents that happen to be in jail on Election Day never lose their voting rights,” Nicole Porter, who leads state and local advocacy at the justice-reform group the Sentencing Project, told me. Ongoing efforts to help potential voters in jail register or request voting materials “are very grassroots conversations,” she said.

In reporting this story, I spoke with people running voter registration, education, and access programs in county jails in California, Illinois, Massachusetts, and Texas. Among organizers, “a lot of the work has been focused on trying to expand rights to [disenfranchised] people in tough states, regressive states,” Porter said. “But it calls into question that we don’t really know what’s happening in jurisdictions where people have the right to vote.”

The chief reason for that obscurity is that the process for voting in jails varies widely: from state to state, from county to county, and even from institution to institution. For example: In California, Illinois, and Texas, detainees have to submit a voter-registration form and an absentee or vote-by-mail request. But in Massachusetts, people in jail are considered “specially qualified”: They don’t have to register to vote before casting a ballot, though the relevant town clerk has to believe that the would-be voter’s legal residence is accurate.

Other states and counties allow voters to list their place of residence as the jail itself. Michelle Mbekeani-Wiley, a former staff attorney at the Sargent Shriver National Center on Poverty Law who led voting efforts in the Cook County Jail, explained that Illinois voters can check a box on their registration form to identify themselves as homeless voters, provided that they include the address of a recognized shelter. Mbekeani-Wiley worked with the county election authorities to ensure that detainees could identify the county jail as their shelter. I asked her if she knew what was happening in the rest of the state. “No, no, we don’t know,” she said. “That would be up to the election authority within that jurisdiction.”