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).
Billy
Billy has been climbing in recent years. All-time it's been given to 528,437 U.S. babies, the 951st most common name by sound today, peaking at 14,327 in 1930, with 639 in 2025.
By sound, Billy also includes the spellings Billie, Billye.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).