Guillermo is a distinctive boys' name in United States, ranking #603 in 2011 with 408 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 41.0%. In 2011, approximately 1 in every 4,654 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.