Reductions in its extent began in 1770, when its southern part became Botetourt County. In 1776 part of western Augusta County, an area also known as the District of West Augusta, became Monongalia County, Ohio County, and Yohogania County (abolished in 1786). In 1778 the portion of Augusta County north and west of the Ohio River became Illinois County (abolished in 1784); the northeastern part of what was remained became Rockingham County, and the southwestern part was combined with part of Botetourt County to form Rockbridge County. In 1788 the northern part of the county was combined with part of Hardy County to become Pendleton County. Augusta County assumed its present dimensions in 1790, when its western part was combined with parts of Botetourt County and Greenbrier County to form Bath County.
Reductions in its extent began in 1770, when its southern part became Botetourt County. In 1776 part of western Augusta County, an area also known as the District of West Augusta, became Monongalia County, Ohio County, and Yohogania County (abolished in 1786). In 1778 the portion of Augusta County north and west of the Ohio River became Illinois County (abolished in 1784); the northeastern part of what was remained became Rockingham County, and the southwestern part was combined with part of Botetourt County to form Rockbridge County. In 1788 the northern part of the county was combined with part of Hardy County to become Pendleton County. Augusta County assumed its present dimensions in 1790, when its western part was combined with parts of Botetourt County and Greenbrier County to form Bath County.