Guillermo is a moderately popular boys' name in United States, ranking #402 in 2001 with 620 recorded births. The name reached its all-time peak in 1998 with 693 births ranking #369. Since 1996, the popularity has decreased by 10.4%. In 2001, approximately 1 in every 3,134 boys born was named Guillermo. STABLE Recent data shows the name is currently stable.