Evolved from our English common law heritage, "castle law doctrine" has long been with us if only in unwritten form. It essentially says it's a manner of self defense if a person kills or injures someone who has illegally intruded in their home or vehicle. As a written declaration, Florida was at least one of the first to pass laws of this nature, but Wikipedia says that, as of May 28, 2010, thirty-one states have some form of Castle and/or Stand Your Ground law.
Ohio's law is of the first type, wherein there is no "duty to retreat" if you're in your home or car, while Kentucky (Here and Here ) and Indiana are both of the latter type, where there no duty to retreat, regardless of where an attack occurs.
Ohio passed its in June 2008, but now USAToday, in discussing a Columbus Dispatch article over the weekend, says "the two-year-old law that was intended to protect Ohio homeowners who shoot intruders in self-defense is instead increasingly being manipulated to help murder suspects avoid taking responsibility for their crimes," according to some prosecuting attorneys.