The late-night sidekick, along with three other people, received a certificate deeming him a Latino Community Treasures during a ceremony that kicked off the start of Latino Heritage Month.
"Guillermo is just one of those household names, figures on national television at a time particularly when Latinos are so under-represented," said Councilmember Monica Rodriguez.
Guillermo started as a security guard on the set of Kimmel's show more than two decades ago. He says Kimmel came to him and offered him a chance to appear in a skit or two.
During Wednesday's ceremony, he thanked Kimmel for giving him a shot at television fame.
"He told me, 'Listen, I'm looking for someone just like you. Not a buff guy, no muscles, nothing like that. I want someone like you with a little belly, someone who's funny, someone who wants to enjoy life,' he said.
"Twenty years later, I'm still here."