Allen Branch is a stream in Washington County, Missouri. It is a tributary of Fourche a Renault.
Allen Branch has the name of John Allen, the original owner of the site.
Allen Branch rises approximately five miles south-southeast of the community of Shirley. The stream flows generally north passing under Missouri Route 8 past Shirley to join the Fourche a Renault about one half mile north of Shirley.
Allen Branch drains of area, receives about 42.7 in/year of precipitation, has a wetness index of 334.51, and is about 88% forested.