Sam says to Dean (to convince him to check on Tasha Banes), "Their mom is on a hunting trip, and she hasn't been home in a week." This echoes one of the first lines of the series, except it was Dean who said to Sam, "Dad's on a hunting trip and he hasn't been home in a few days". This line convinced Sam to come with him to find their father, which jump-started the entire series.
When Mary phones Dean and gets his voicemail, the prompt is, "This is Dean's other other cell, so you must know what to do". This has been his voicemail since practically the beginning of the show, a span of almost a decade.
Linda Darlow, who plays Demon Borrower Witch, played Ezra Moore in Time After Time (Season 7, Episode 12).
This episode takes place in Rock River, Wyoming.