Astragalus proimanthus is a species of flowering plant in the legume family known by the common name precocious milkvetch. It is a narrow endemic, occurring in an area of less than 320 acres near the town of McKinnon in southwestern Sweetwater County, Wyoming. It has four known populations, including one large population of more than 20,000 individuals, and is classified by NatureServe as G1 (critically imperiled) "because of extreme rarity".