Guillermo is a moderately popular boys' name in United States, ranking #428 in 2003 with 595 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 14.0%. In 2003, approximately 1 in every 3,320 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.