Is it illegal for an Adult Family Care Home to request a security deposit prior to a resident moving in?

It is not illegal.

That would largely depend on the laws in your state and perhaps community. You might check with your local legal aid office and/or the local Agency on Aging.

I don't know why it would be illegal. Apartments ask for that kind of deposit in advance of moving in all the time.

To my knowledge, this has been a policy that has always been in existence.