Missouri residents are familiar with a big bill that arrives in their mailboxes every December.
Personal property taxes can cost hundreds of dollars depending on the type of vehicle owned.
In St. Louis County. the assessor estimates "one percent" of drivers register their cars in Illinois to avoid paying the tax in Missouri.
"It's enough to add up to millions lost to fire departments, school districts and public servants," said St. Louis County Assessor Jake Zimmerman.
He added, "It outrages me."
It's against the law, and now an Illinois man was convicted on federal charges for helping Missouri residents register their cars across the river.
Melvin Harmon is referred to in a federal indictment as "The Plate Man."
According to the federal indictment, Harmon was an employee at an Illinois motor vehicle registration facility.
Harmon was accused of charging Missouri residents up to $700 to obtain Illinois license plates.
The indictment says, "Melvin Harmon and his co-conspirators solicited individuals directly or through flyers."
Harmon was facing several counts including conspiracy to defraud and mail fraud. He was recently convicted.
In addition to obtaining fraudulent plates for Missouri residents, the indictment alleges Harmon "caused the mailing of fraudulent motor vehicle titles from the Secretary of State for Illinois to lien holders located in various states."
News 4 attempted to interview Harmon after he appeared in federal court.
Harmon did not answer most questions but at one point during an exchange with Investigative Reporter Chris Nagus Harmon said, "At some point the truth will come out."
According to Zimmerman, his office has the power to double someone's assessment if they're caught cheating.
Sentencing is scheduled for August. He could face 20 years in prison.
If you know someone that lives in Missouri but registers their cars in Illinois you can report it to the Missouri Department of Revenue.