How to read the band →
Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Millie
Millie has been climbing in recent years. All-time it's been given to 49,485 U.S. babies, the 260th most common name by sound today, peaking at 3,466 in 2025, with 3,466 in 2025.
By sound, Millie also includes the spellings Milly.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).