While director Mark G. McFarlane, production assistant Dominic Moss and camera assistant / Stills photographer David C. Box all attended college together, they were completely unaware that actor Martin Haddow was attending the same college at the exact same time. They all only learned of this when relaxing after the first day of shooting.
On the final day of principal photography while on location out in the countryside, director Mark G. McFarlane completely tore his jeans on a barbed wire fence. Fortunately he was wearing shorts underneath, and shooting was able to continue successfully.
The bench featured where the Courier and the Stranger first meet now no longer exists, having been replaced with a newer seat shortly after filming. Many of the places featured in the film now no longer exist, including the campfire shelter, New Cumnock Games Hall (filmed but cut), and the Arthur Memorial Church (filmed but cut).
Forth McCarthy is named for Cormac McCarthy, author of 'The Road', which was one of the inspirations for 'A Letter from Perdition'. Additionally, Coat Hill is named for John Hillcoat, director of the 2009 film adaptation.
The Stranger's line "Only misfires on me I'm afraid. Delivery boy." is an homage to Randall Flagg in Stephen King's 'The Dark Tower' series of books. Specifically his line in 'The Dark Tower IV: Wizard and Glass' - "Only misfires against me, Roland, old fellow". The Stranger and Flagg share similar characteristics, and the world of 'A Letter from Perdition' is influenced by the world of King's series.