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).
Kelly was more common in the past and has since settled at a lower, steady level. All-time it's been given to 747,877 U.S. babies, the 1,055th most common name by sound today, peaking at 27,067 in 1969, with 471 in 2025.
By sound, Kelly also includes the spellings Kelli, Kelley, Kellie, Keli, Kellee, Kellye, Kelle.