The name reached its all-time peak in 2021 with 5 births ranking #13425. STABLE Recent data shows the name is currently stable.
Millie is a warm vintage short form that now often stands as a given name in its own right. Its exact traditional meaning depends on which longer name family sits behind it.
Its rise fits the broad return of nickname-style vintage names that feel affectionate and energetic. Millie works especially well because it is cheerful without feeling flimsy.