The Locative case exists for all names of towns and cities.  The word domus also has a locative form.  The locative is the same in form as the genitive (singular) for singular place names of the 1st and 2nd declensions and the ablative (plural) for plural place names.  For all place names of the third declension, the locative is the same as the ablative (singular and plural) in both the singular and plural.  Here are some common forms for examples: