Boundary is a large hamlet in South Derbyshire situated between the towns of Swadlincote and Ashby de la Zouch on the A511 route. It is west of the village of Smisby and forms part of the county border with Leicestershire, hence its name. Residences on the north side of the A511 lie in Derbyshire and those on the south side lie within Leicestershire. The hamlet falls within the civil parish of Smisby.