I have an opossum that is getting into my crawlspace through a groundhog hole. If I hire a wildlife removal contractor to catch it, can I just plug up the hole and release it back onto my property. Or must it be euthanized?

It can be released onto your property. Just be sure the groundhog burrow is filled in first. If you wanted to trap and release the opossum yourself, you'd just need a permit (free) from the IDNR district wildlife biologist. Let me know if want more information about this option, or if you need help locating a local NWCO.