The owner of a nearby home went to jail and now I'm seeing people around the house. I was wondering how do you go about claiming what's in the house.

Are you a relative? Do you have any property in the house you can claim? If not, mind your own business. If you think people are looting the house, call the police.

Just because the owner is in prison doesn't make his stuff free for the taking. If you help yourself to the contents of the house, you might join the owner- in prison.