According to STATSIndiana, In 2007, Indianapolis/Marion County had an estimated population of 876,804. Of that number 232,607 were below 18 years of age, for a total of 644,197 people in Marion County/Indianapolis 18 or over and thus eligible to vote. (Indiana allows felons to vote as long as they are not incarcerated).
So we have 644,197 people eligible to be registered in Marion County/Indianapolis, and 677,401 people registered. Congratulations go to Indianapolis for having 105% of its residents registered!