What are squatters rights? The house next door has been abandoned for 18 months... read detail, please.?

The city mows the back yard every once and a while to keep it nice, but nobody lives there. If my family moves there and fixes up the house really nice on the inside, could we be sent to jail for living there? Or would they just kick us out? Or can they even do anything at all; no one knows who owns it in the neighborhood!