"I Knew You When" is a song written by Joe South and was recorded by Billy Joe Royal for his 1965 album, Down in the Boondocks. The song reached No. 14 on the Billboard Hot 100 in 1965. The song went to No. 1 on the Canadian music chart in November 1965.
Joe South would later record his version of the song for his 1969 album, Games People Play.
Donny Osmond released a version in 1971 as the B-side of "Hey Girl" that went to No. 9 on the Hot 100 as a double-sided hit.
Linda Ronstadt recorded a version for her 1982 album, Get Closer. It reached No. 37 on the Hot 100 chart as the album's second single. It also reached No. 29 on the adult contemporary chart, No. 84 on the country chart, and No. 90 in the UK.