Petersburg, the county seat of Grant County, is situated on the South Branch of the Potomac River near the Hardy County border, 30 miles from the Virginia line. The town is located at the junction of U.S. 220 and state routes 42 and 28. The 2010 population was 2,467.

Settled in 1745 as Lunice Creek, its name was changed to Petersburg, probably in honor of early merchant Jacob Peters, then to Grant Court House when it became the county seat in 1870, and finally back to Petersburg. The town has a hospital, city library, volunteer fire department, newspaper, high school and elementary school, nine churches, several restaurants and motels, a variety of retail stores, and a new city park. Winter weather is mild and summers warm but pleasant. Grant County Airport is nearby.

Widely known for its excellent trout fishing, Petersburg's proximity to the river, Smoke Hole Canyon, Spruce Knob, Seneca Rocks, and the North Fork Mountain attracts many visitors. Annual celebrations include the Spring Mountain Festival and the Tri-County Fair (shared with Hardy and Pendleton counties). The Petersburg Wave, a powerful seasonal updraft, makes Petersburg popular with glider pilots.