Guillermo is a moderately popular boys' name in United States, ranking #476 in 2008 with 583 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 15.8%. In 2008, approximately 1 in every 3,499 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.