| Cillian | Sullivan | |
|---|---|---|
| Meaning | Bright-headed; church | dark-eyed (disputed) |
| Origin | Irish | irish |
| Gender | Boy | Boy |
| Pronunciation | KIL-ee-un | SUHL-ih-vuhn |
| Syllables | 2 | 3 |
| First appeared | 1995 | 1884 |
| Peak year | 2024 (668) | 2025 (1,083) |
| In 2025 | 595 | 1,083 |
| Trend | Near its peak | Near its peak |
Source: US Social Security Administration.
| Decade | Cillian | Sullivan |
|---|---|---|
| 2020s | 2,662 | 5,564 |
| 2010s | 1,204 | 6,428 |
| 2000s | 208 | 2,135 |
| 1990s | 10 | 535 |
| 1980s | 0 | 83 |
| 1970s | 0 | 86 |
| 1960s | 0 | 85 |
| 1950s | 0 | 129 |
| 1940s | 0 | 114 |
| 1930s | 0 | 110 |
| 1920s | 0 | 141 |
| 1910s | 0 | 122 |
| 1900s | 0 | 10 |
| 1890s | 0 | 63 |
| 1880s | 0 | 30 |
Cillian is linked to “bright-headed” and to cill, “church” or “monastery.”
Anglicized from Irish O Suilleabhain, from 'suil' meaning 'eye' plus a second element usually read as 'dubh' (dark/black), giving 'dark-eyed'. The second element is disputed; alternative readings give 'one-eyed' or 'hawk-eyed', so the 'dark' sense is probable rather than certain.
Sullivan is more popular than Cillian today: about 1,083 US babies were given the name Sullivan in 2025, compared with 595 named Cillian.
Cillian means Bright-headed; church (Irish origin), while Sullivan means dark-eyed (disputed) (irish origin).
In US records, Cillian first appears in 1995 and Sullivan in 1884, so Sullivan has the longer recorded history.