Q. Which is correct, “in the peninsula” or “on the peninsula”? Why?
A. It’s possibly a bit more logical to refer to someone or something being on a peninsula than in one, on the principle that we tend to live on land masses but in countries, provinces, states, cities, and the like. So, for example, one might refer to someone who lives in Mexico but on the Yucatán Peninsula—or in New York but on Long Island. But if you’re an editor, keep an open mind. Prepositions are notoriously variable; they depend greatly on local usage and personal preference, and usage can change over time.