This article discusses the earliest attestations and history of various English indefinite hyperbolic numerals such as zillion, jillion, and umpteen, identifying them as a previously unrecognized category of contemporary English words with a peculiarly American emphasis. Umpteen originated in the late 1870s but became normative in the Midwest in the 1890s, not as World War I British soldiers' cant as frequently claimed. Zillion first flourished in African American English in the 1920s, while jillion originated independently in Texas around the same time. These ought to be regarded as a contemporaneous cluster of locally developed words within specific discourse communities rather than random nonce inventions. Since 1985 a massive expansion has occurred in the lexicon, primarily using the emphatic prefixes ka-, ba-, and ga-. Interviews conducted with African American youth in 2009–10 suggest that zillion may be acquiring a fixed numeral meaning (following trillion) among some speakers. Indefinite hyperbolic numerals represent a lexical category newly, promiscuously, and playfully developed in late nineteenth- and twentieth-century Englishes, in a discursive environment where numerical reference had become normative.