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).
Kevin is now well below its former popularity. All-time it's been given to 1,202,257 U.S. babies, the 409th most common name by sound today, peaking at 30,943 in 1963, with 1,643 in 2025.
By sound, Kevin also includes the spellings Keven, Kevan.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).