Gillermo is a name of Spanish origin, derived from the Germanic element "will" and the Germanic element "helm," meaning "protection" or "helmet." It is the Spanish form of the German name Wilhelm. In English, it may be spelled Guillermo or Gillermo. This name has been popular in Spain for centuries and is often associated with notable figures such as Guillermo Tell, the legendary Swiss folk hero who inspired a famous opera by Gioachino Rossini. However, it is not widely used in English-speaking countries.
The name Guillermo experienced fluctuations in popularity over the years, with a notable peak in the late 1940s and early 1970s. The highest number of births was recorded in 1972 with 18 babies named Guillermo. However, there were periods where the name's popularity declined significantly, such as between 1960 to 1966, when there were fewer than 10 births each year. Overall, a total of 633 children have been named Guillermo over the period recorded.