The term "Megalopolis" (with a capital "M") was originally used to refer to the US Eastern Seaboard urban agglomeration of the five cities of Boston, New York, Philadelphia, Baltimore, and Washington (as well as such smaller centers such as Providence, Hartford, and Wilmington). It has since been extended (with a lower-case "m") to mean any large decentralized polynuclear urban area composed of several (usually formerly separate) cities.

Examples of megalopoli outside of the original Megalopolis include the Ruhr region of Dortmund-Duisburg-Essen-Düsseldorf-Köln in Germany, and "Canada's Mainstreet", Québec-Montréal-Ottawa-Toronto-Windsor (and perhaps Buffalo and Detroit in the US).

California's "San-San" region stretching from San Francisco to San Diego and including Oakland, San Jose, Los Angeles, and San Bernardino is sometimes named as a megalopolis, as is on rare occasion the Vancouver-Seattle-Tacoma-Olympia-Portland-Salem-Eugene urban corridor in the Pacific Northwest.