Arlington County was originally named Alexandria County. It was formed from a part of Fairfax County that was ceded to the U.S. government in 1789 but was returned to Virginia in 1846. The county name was changed in 1920 to Arlington, the name of the Custis family mansion (former home of Robert E. Lee), which is located in the county.

The 1870 Virginia Constitution required that each county in the state be divided into no less than three townships (see Article VII, section 2). Based on the New England administrative organization of a county, each township would elect the administration officials for the offices of supervisor, clerk, assessor, collector, commissioner of the roads, overseer of the poor, justice of the peace, and constable. The supervisors of each township would comprise the board of supervisors for the county, and would be responsible for auditing the county accounts, examining the assessors' books, regulating property valuation, and fixing the county levies. The Acts of Assembly provided that each township be divided into school and electoral districts (see Acts of Assembly 1869-1870, Chapter 39). A constitutional amendment in 1874 changed the townships into magisterial districts and each district elected one supervisor, three justices of the peace, one constable, and one overseer of the poor. The supervisors of the districts made up the county board of supervisors whose duties were identical as those set out in 1870. The published Acts of Assembly appended a list of township names by county following the acts for every year that townships existed in Virginia.