Guillermo is a moderately popular boys' name in United States, ranking #434 in 2005 with 616 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 11.0%. In 2005, approximately 1 in every 3,242 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.