I do know that Michigan law prohibits carrying in a church, even if you have a permit. However, I'm told that if you have the permission of the pastor, it's OK. I haven't attempted to verify that by looking up the law. I suggest anyone living in Michigan check the law.
In Ohio, the law prohibits carry in church, unless you have the permission of the pastor. Unfortunately, the bishop of the Cincinnati diocese has forbidden all pastors to give that permission. So in the Cincinnati diocese, carry in church is illegal. I know people who carry anyway, but strictly speaking, they're in violation of the law.
I live in Michigan and I checked the law. You may carry at church at the church leadership's discretion. I say leadership rather than the minister because at some churches (like mine) the minister serves at the pleasure of the elders. He doesn't have the authority to make a decision like that. The law takes that into account.