Cincinnati is in Hamilton County, Ohio. In their locality database, Ancestry has not had Cincinnati in Hamilton County for over a year.
This error is easily demonstrated by entering "Cinci..." on the main search page and Ancestry will currently prompt with Cincinnati, Madison, Ohio. Madison County is about 180 miles away and has historically never been associated with Cincinnati.
In Ancestry record collections including "Ohio Death Certificates," when the locality is Cincinnati, Ohio, Ancestry will assist the researcher by standardizing the locality, using their locality database. Cincinnati, Ohio now automatically becomes Cincinnati, Madison, Ohio. For most of the past year, Ancestry had Cincinnati in Clermont County, Ohio.