More Hoosiers are registered already this year than in any election for more than a decade.
The Indiana State Police investigation is looking into whether fraudulent names or addresses were used in registering voters.
Investigators believe more than 100 voter registration forms could have been compromised.
According to the Indiana Secretary of State, 200,000 more residents have registered to vote in this year's presidential election than eight years ago.
Secretary of State Connie Lawson says the spike is thanks to a Facebook reminder posted over the weekend.
The forms were among thousands submitted by the Indiana Voter Registration Project in Marion and Hendricks counties.
Officials say the upcoming presidential primaries led to a vast increase in the amount of voter registrations in certain counties in the past week.
The number of Indiana children in need of foster care rose has risen significantly.
The last day to register to vote for the upcoming municipal elections is April 6. Primary day is May 5.
A Pew Charitable Trusts report shows Indiana has improved its election performance but is still fares poorly compared to other states.