Subscribe to The Chicago Manual of Style Online
Possessives and Attributives
Q. Should the possessive form of Los Angeles include the extra s? As a Spanish term, the city’s name is a singular noun, plural in form, but if we consider it fully anglicized, does it then count as a regular singular? Or does the plural form carry through?
A. It’s true that city names that include a plural word in English can drop the extra s when forming the possessive: Twin Groves’ population. But city names are by default singular (Twin Groves is a small city), and a guideline for styling non-English names in English should not depend on a writer’s knowledge of their meaning in the original language. Thus the possessive of Los Angeles in Chicago style follows the guidelines for singular possessives in English: Los Angeles’s.