Ustylug – one of the ancient towns in Volyn. It has been known since the annals (1150). Later it was called in different ways – Ustilogov (1545), Uschilug (1576), Uscilug (1577). At some time, the town was even named Ruzhyiampol (1765), the name was gained in the 18th century in honor of Rozalia Rouge Potey from Zagorovsky with the emblem of Golden Rouge on a blue background.