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).
Josiah climbed for decades and has been a steadily popular name ever since. All-time it's been given to 165,600 U.S. babies, the 84th most common name by sound today, peaking at 7,945 in 2017, with 6,474 in 2025.
By sound, Josiah also includes the spellings Jasiah, Jesiah, Josiyah.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).