I'm Shocked!
The Penn News stuns the senses of its readers with Penn Researchers Document Large-Scale Voter Registration Problem: More Voters Registered Than Eligible to Vote:

More people are registered to vote than there are residents of legal voting age in two states and 241 counties in the United States.

Researchers at the University of Pennsylvania Fels Institute of Government discovered the voting over-registration problem while conducting the Carnegie Corporation funded Fels Voting Index project, an annual ranking of states according to the accuracy, accountability and accessibility of their voting systems.
...
When researchers compared the EDS figures with data for eligible voting-age residents drawn from the 2000 U.S. Census, they determined that in the 2000 presidential election there were more registered voters than voting-age residents in Alaska and Montana and that 32 states have at least one county with more registered voters than eligible voters. This determination led them to the conclusion that registration rolls in these, and many other counties and states, are grossly inaccurate.

Maybe dead people don't fill out their census forms properly?

Actually, I can think of several explanations for this besides the obvious, including the fact that folks in Alaska and Montana might not be overly enthusiastic about the census. But I would like to know the list of counties. The researchers also ought to look close to home - as I recall, Philadelphia is famous for having more voters than voting age residents. They sum up with

Over-registration creates opportunities for voting fraud and should be eliminated.

Leaping lizards, Sandy!