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).
Spencer
Spencer is now well below its former popularity. All-time it's been given to 133,001 U.S. babies, the 600th most common name by sound today, peaking at 4,892 in 1998, with 1,159 in 2025.
By sound, Spencer also includes the spellings Spenser.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).