One in 7 counties in Illinois has more voters on the electoral rolls than the number of adult residents the U.S. Census tallied, a new study has found. The state’s Board of Elections is trying to determine why the figures in 14 counties are so out of whack, according to the the Quad-Cities Dispatch-Argus.

The northwestern Illinois paper, which covers two of the counties, reports that there are 125,875 registered voters in Rock Island County, but only 114,359 residents over 18. Much smaller Mercer County has 14,295 voters and 12,714 adults, according to the census.

Rock Island County Clerk Karen Kinney said there could be several reasons for the discrepancies. "People move out of Rock Island County, and nobody notifies us," she said. "People die and no one notifies us.â€