Guillermo is a distinctive boys' name in United States, ranking #902 in 2025 with 264 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 61.8%. In 2025, approximately 1 in every 6,470 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.