The name Milly is a girl's name . Milly and discussed in our forums with posts like "Girls Makeover - Two Middles".
From the experts:
Milly and her more popular sister Millie are adorable Old Lady nickname-names springing back to life. Nearly 100 baby girls were named Milly, just Milly, last year, and Millie is in the US Top 500. Milly is the Molly of the new generation.