Grant County Courthouse, also known as the Old Grant County Courthouse, is a historic county courthouse located at Petersburg, serving Grant County, West Virginia. The original section was built in 1878–79 and expanded in 1909. It is composed of 3 two-story brick rectangles consisting of a large center section with lower and narrower wings. The building is styled with Neo-Colonial design features. The center section features a two-story projecting portico with pediment and supported by four Corinthian order fluted columns.
It was listed on the National Register of Historic Places in 1979.