This is the only surviving courthouse by Mercer in Southwest Virginia. His courthouse of 1834 in Smyth County was demolished in 1905. The Giles County Courthouse's composition of a central block with flanking two-story wings epitomizes a design popularized in Southwest Virginia by builder James Toncray (
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,
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). The courthouse features a hipped roof with an octagonal domed cupola above the unusually tall central block, as well as a large arched multipane fanlight over the central entrance. An arched window on the second story was blocked up around 1900, when the attenuated Corinthian portico was added to the courthouse's facade. A building of 1937 housing the sheriff's office and jail adjoins the courthouse.