I originally missed the fact that the student is 25. He may not qualify as his parent's dependent.
There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit and student status test, a relationship test and a residence test.
He is too old to be a QC. So, now there is an income test to be a dependent. A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:
- Closely Related OR live with the taxpayer ALL year
- His/her gross taxable income for the year must be less than $4300 (2020).
- The taxpayer must have provided more than 1/2 his support
In either case:
- He must be a US citizen or resident of the US, Canada or Mexico
- He must not file a joint return with his spouse or be claiming a dependent of his own
- He must not be the qualifying child of another taxpayer
A QC would have to be considered an OH resident, because living with the parent is a QC rule. However, a qualifying relative does not have to reside with the parent, so as @KathrynG3 said, there are circumstances where he could be considered an IA resident.
