St. Vrain is a ghost town located in Weld County, Colorado, United States.

The town was located adjacent to the frontier trading post of Fort Saint Vrain northeast of the confluence of Saint Vrain Creek and the South Platte River.

The historic Saint Vrain was known as Veranus of Cavaillon, a sixth-century French Christian bishop.

After the fort closed, the area remained an important meeting point and place of refuge.

In 1868, the Weld County seat was moved to Latham (in present-day Greeley.)