Mosby Street, the Mosby Court public housing development, and the former Mosby Middle School were all named for Benjamin Mosby, a developer who helped lay out the streets of Union Hill in 1805.
From the RPS history of Mosby Middle School:
Mosby School was named for Benjamin Mosby, a realtor who developed the area early in the nineteenth century. Part of this area became known as Union Hill and part as Howard’s Grove, in which (prior to annexation in 1906) a four-room high school was maintained by Henrico County on Spottswood Street.
Given the city’s connection to the Civil War, it is a common misconception that the local use of Mosby is a reference to the Confederate hero John Singleton Mosby.