Cillian vs William
How Cillian and William compare across 146 years of US Social Security Administration baby-name records — popularity history, peak years, current rank, and which name overtook which.
William
Male · German
Meaning: Resolute Protector: Will. For A Long Time After The Norman Conquest In A.D. 1066 Many English Boys Were Given Some Form Of William The Conquer's Name. William. The Firstborn Son Of Prince Charles Is Named William.
US Popularity History — Side-by-Side
Annual US births named Cillian (boys) vs William (boys), from US Social Security Administration national records.
Source: US Social Security Administration. Names appearing fewer than 5 times per year are suppressed by SSA.
Quick Stats
| Metric | Cillian | William |
|---|---|---|
| Peak year (most US births) | 2024 — 668 boys | 1947 — 67,001 boys |
| Peak rank | #463 | #4 |
| Most recent rank (2025) | #507 (595 births) | #9 (10,545 births) |
| Total US births since 1880 | 2,659 | 4,199,549 |
| Last 10 years (2016–2025) | 2,659 | 127,126 |
Peak comparison takeaway
At its all-time peak, William reached 67,001 US births in 1947 — 66,333 more than Cillian's peak count.
Strongest States — Last 10 Years
States where each name ranked highest, from SSA's state-level dataset. Lower average rank = name appears closer to the top of that state's boys-name list.
Cillian — top 5 states
| # | State | Avg rank | Births |
|---|---|---|---|
| 1 | New Hampshire | #239 | 15 |
| 2 | Massachusetts | #354 | 141 |
| 3 | Connecticut | #413 | 40 |
| 4 | Oregon | #476 | 30 |
| 5 | Minnesota | #509 | 31 |
William — top 5 states
| # | State | Avg rank | Births |
|---|---|---|---|
| 1 | Alabama | #1 | 3,254 |
| 2 | South Carolina | #2 | 2,682 |
| 3 | Mississippi | #2 | 1,586 |
| 4 | Tennessee | #2 | 4,126 |
| 5 | Georgia | #2 | 5,159 |
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Data & methodology
Source: US Social Security Administration national baby names dataset 1880–2025 (CC0 public domain). Names with fewer than 5 occurrences in a given year are suppressed by SSA. State-level coverage runs 1910–2025. Crossover detection compares annual birth counts (not ranks) for each year both names appear. Methodology: see full notes. More comparisons →