Guillermo is a distinctive boys' name in United States, ranking #506 in 2009 with 534 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 22.8%. In 2009, approximately 1 in every 3,714 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.