I live in Indiana, my check is garnished for child support all my kids are of age and out of college, how can I stop payments?

Are there any arrears still owed or are you fully up to date?

If your paycheck is being garnished, then you have to contact the agency collecting the support. Show them the original support order and asl what has to be done to stop the garnishment and get a refund of any overpayment.

As noted, they may still be collecting for arrears that occurred earlier, but only the agency doing the collecting can tell you when it will stop or how to stop it. If you are not sure of who is collecting your payroll department should be able to tell you where the payments go. Its probably here: http://www.in.gov/dcs/support.htm

but only the agency doing the collecting can tell you when it will stop or how to stop it.

I'm assuming that this garnishment is being done pursuant to a court writ (of garnishment, perhaps). If so, OP could apply to the court to quash the writ, showing that the child support obligation is satisfied.

Some child support agencies seem to have the power to issue writs of garnishment without a court order.