Kimmel opened the show with a monologue that honored their friendship, and Willard's undeniable comic genius.
"He was more than just funny. He had a light inside him; you could see a glint of it in his eyes. And it made everyone around him happy," Kimmel said of the Best In Show star, who died Friday at the age of 86.
Kimmel shared a sweet story about working with Willard years ago when they were shooting a sketch in his house, and the affable comic was "uncharacteristically down" and upset about his wife having thrown away their Christmas tree -- despite the fact that it was already June.
According to Kimmel, Willard said he'd exercise by sawing bits of the tree, and he got depressed when his wife, Mary, had gotten rid of it. So, to cheer him up, Kimmel managed to find a pine tree the same day and had it sent to his house, which cheered him up entirely.
"In a lot of ways, Fred Willard was like a Christmas tree in June -- a little weird, familiar but still surprising to see it, full of good memories and you're just instantly happy that it's there," Kimmel said.
While Kimmel had worked with Willard many times over the years, their collaborations grew much more frequent in 2018, after Mary -- his wife of 50 years -- had died. Kimmel said he wanted to find something to work with Willard on, and Donald Trump's announcement of his planned "Space Force" proved to be the perfect opportunity.
Kimmel discovered that Willard has starred in the 1978 TV movie Space Force, and asked him to reprise his role from the little-known film, and the sketch was a bizarre delight.
"After that, we started putting him in everything, every sketch," Kimmel said, smiling. "There were days when I would get different writers pitching five different bit ideas for Fred."
"Sometimes he'd be in two bits per monologue, and I couldn't choose between them," he continued. 'We could not get enough Fred."
The host went on to say that, no matter the circumstances, Willard was always a professional and absolute delight.
"He never had any time to prepare for these bits. We'd call him at noon, and say, 'Hey, today you're gonna be a boat captain.' He'd say, 'Aye-aye,' and he'd be on set by two," Kimme recalled. "We'd do one run-through of the script…. And then he and I would do it with no rehearsal live in front of the audience and he nailed it every time."
Kimmel wrapped up the touching monologue with a montage of snippets from a few of his his favorite sketches that Willard shined in like only he could.
Throughout the rest of the evening -- which was entirely dedicated to the comic star -- Kimmel spoke with several of the actor's longtime friends and former co-stars, who reflected on his life and legacy.
Kimmel spoke to some of Willard's most frequent collaborators, including Catherine O'Hara, Eugene Levy and Martin Mull, as well as director Christopher Guest, who all reminisced about how Willard elevated everything he was a part of.
Modern Family stars Ty Burrell and Julie Bowen -- who worked with Willard on the hit sitcom -- also joined the retrospective episode, alongside Ray Romano, who'd worked with Willard on Everybody Loves Raymond, and iconic TV legend Norman Lear.