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).
Mathias has been climbing in recent years. All-time it's been given to 29,220 U.S. babies, the 458th most common name by sound today, peaking at 1,941 in 2025, with 1,941 in 2025.
By sound, Mathias also includes the spellings Matthias.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).