Saint Folcwin or Folcuin (Latin: Folquinus, Folcwinus, Folcvinus;[1][2] Old Dutch: *Folkwin; French: Folquin) (d. 15 December 855) was a Frankish abbot, cleric, and Bishop of Thérouanne (appointed 816).
Folcwin was born to Hieronymus, son of Charles Martel, and his wife Ercheswinda (Ermentrudis).
He was appointed bishop of Thérouanne in 816 and confirmed by Louis the Pious; he was consecrated in 817 by the Archbishop of Reims, likely Ebbo.
Charles the Bald appointed him as Missus dominicus for one of the twelve West-Frankish missatica, one which apparently overlapped mostly with his diocese.
The earliest evidence of a cult is found in the work of his relative, Folcuin, abbot of Lobbes,[3] who produced the Gesta abbatum Sithiensium (or Gesta abbatum Sancti Bertini, "Deeds of the Abbots of Saint-Bertin"), a combination of chronicle and cartulary.