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).
Brennan
Brennan is now well below its former popularity. All-time it's been given to 49,086 U.S. babies, the 1,439th most common name by sound today, peaking at 2,203 in 2009, with 272 in 2025.
By sound, Brennan also includes the spellings Brennen, Brennon.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).