The MINIMUM full year penalty for not having health insurance is $695, but it is also based on income, so it could be higher. If it was only part of year, the penalty is prorated. For example, the minimum penalty for 9 months would about $521.
So if you actually claim him as a dependent, you will owe that penalty. However, claiming him as a dependent MIGHT save you more than that, depending on what your income is. If you were in the 25% tax bracket, claiming him as a dependent would likely save about $1000, plus State taxes.
If the penalty is higher than what you would save, you *MIGHT* be able to avoid the penalty by not claiming him. This falls into a "gray area", but my opinion is that you would avoid the penalty if you did not actually claim him. However, I hope the tax savings of claiming him will be larger than the penalty, so hopefully you won't need to deal with that.
As a side note, he may qualify for free health insurance through Medicaid. However, that depends on which State he lives in.
