list unique entries

I have a weblog (EE1 site) that will list offices by state. I’m trying to create a list on the previous page that simply lists all the states with an entry based on a custom field in each office entry. Is there a way to ensure I don’t get a state listed multiple times if that state has more then one office? I could do this with two weblogs but I’d prefer to avoid having to create a weblog to just store state names.