Astragalus barrii is a species of flowering plant in the legume family known by the common name Barr's milkvetch. It is native to the United States, where it is a "regional endemic", occurring in parts of southwestern South Dakota, northeastern Wyoming, southeastern Montana, and Nebraska. This plant was first collected in 1900 in Wyoming. It was described as a species in 1956 and named for the botanist and cattle rancher Claude Arno Barr (1887–1982).