Agonopterix lythrella is a moth in the Depressariidae family. It was described by Walsingham in 1889. It is found in North America, where it has been recorded from Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Brunswick, New Hampshire, New York, North Carolina, Nova Scotia, Ohio, Ontario and Saskatchewan. The larvae feed on Lythrum alatum, Hypericum punctatum and Hypericum virginicum.