The story
From Ancient Greek λαός /laos/ (people) + ἀριθμητικός (arithmetics). Coined in “Larithmics: An Addition to Sociological Terminology” by American sociologist Henry Pratt Fairchild in the “American Journal of Sociology”, Vol. 36, No. 2 (Sep., 1930), pp. 278-281; published by: The University of Chicago Press (archive: https://www.jstor.org/stable/2766383).
Etymology from Wiktionary, CC BY-SA 4.0.