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).
Sydney
Sydney is now well below its former popularity. All-time it's been given to 320,660 U.S. babies, the 511th most common name by sound today, peaking at 13,455 in 2000, with 1,184 in 2025.
By sound, Sydney also includes the spellings Sidney, Sydnee, Sydni, Sydnie, Cydney.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).