This episode was originally written for Ringo Starr. However, since the crime involved the victim being shot in an alley, the producers thought it too reminiscent of John Lennon's assassination. They also considered singers Brian Wilson and James Taylor before deciding to go with Willie Nelson.
A reference is made to Willie Nelson's famous pot smoking when, in the bus, Monk asks him, "Do you smell something?" and Willie answers, "No... And neither do you."
Mr. Monk and the Red-Headed Stranger (2002) has a famous singer, Jackie Richardson, who plays Wendy Maas. She is a prominent singer in her own right and was a member of the girl group The Tiaras in the 1960s. She was born in Pennsylvania in 1947 and moved to Toronto (where this episode was shot) in 1954.
When Benjy asks Sharona if Willie Nelson has ever been on MTV, she answers "no". He was in fact on MTV in 1985 as part of USA for Africa, singing "We Are the World."