Guillermo is a moderately popular boys' name in United States, ranking #454 in 2007 with 610 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 11.8%. In 2007, approximately 1 in every 3,402 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.