Where do I report rental income from a mother in-law

Do you really have a formal rental agreement with your family member and you rent to them for fair market value ?  Or is this just a cost sharing situation ?

Its not a family member, it is someone we advertised to and rented it out to for fair market value.

Ok ... so you are renting out a "mother in law" appt  not to your MIL.    It goes on the Sch E ... follow the interview in the rental section carefully.  You will need to prorate the common expenses and remember you are NOT using the property for personal use at all .. it only has rental days.

You enter it in the rental section, definitely.