Guillermo is a distinctive boys' name in United States, ranking #553 in 2010 with 457 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 34.0%. In 2010, approximately 1 in every 4,198 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.