Most conservative major city on the East Coast?

[TJ in Oregon]

North of DC would most likely be Buffalo.

Cincy is included in the list. While I'm not sure by what standard in hell it could be considered an East Coast city - but then Buffalo shouldn't be either - it clearly wins of the available choices. Unless it's deemed to be south of DC.
As to cities actually on or near the coast and north of DC, the answer is Baltimore followed by New York City.

Yeah, Cincinnati is way more conservative than others on that list north of DC. It's probably the third or fourth most conservative on that list outright even.(not that Cincinnati or Cleveland or Columbus or Detroit can even remotely be considered East Coast) The Cincinnati area is the type of area where voting results look an awful lot like a racial map. Once you leave the poor urban areas, the people become very Republican very fast. Conservatism is a part of the fabric of that town, even if it is a lot different from most of the southern cities you would call conservative in that its politics stem from the major immigrant group being German Catholics rather than some of the more Democratic groups, combined with the Taft political dynasty. There's a saying that if the world ended, Cincinnati is the place to be because it wouldn't happen there for ten more years.