| Cillian | Kieran | |
|---|---|---|
| Meaning | Bright-headed; church | little dark one |
| Origin | Irish | irish |
| Gender | Boy | Boy |
| Pronunciation | KIL-ee-un | KEER-uhn |
| Syllables | 2 | 2 |
| First appeared | 1995 | 1918 |
| Peak year | 2024 (668) | 2025 (817) |
| In 2025 | 595 | 817 |
| Trend | Near its peak | Near its peak |
Source: US Social Security Administration.
| Decade | Cillian | Kieran |
|---|---|---|
| 2020s | 2,662 | 3,946 |
| 2010s | 1,204 | 5,282 |
| 2000s | 208 | 4,412 |
| 1990s | 10 | 2,177 |
| 1980s | 0 | 610 |
| 1970s | 0 | 415 |
| 1960s | 0 | 374 |
| 1950s | 0 | 222 |
| 1940s | 0 | 81 |
| 1930s | 0 | 48 |
| 1920s | 0 | 38 |
| 1910s | 0 | 8 |
Cillian is linked to “bright-headed” and to cill, “church” or “monastery.”
Anglicized from Irish Ciaran, a diminutive of 'ciar' meaning 'black, dark', giving 'little dark one'. Borne by several early Irish saints.
Kieran is more popular than Cillian today: about 817 US babies were given the name Kieran in 2025, compared with 595 named Cillian.
Cillian means Bright-headed; church (Irish origin), while Kieran means little dark one (irish origin).
In US records, Cillian first appears in 1995 and Kieran in 1918, so Kieran has the longer recorded history.