Wetzel County is a county in the U.S. state of West Virginia. As of the 2020 census, the population was 14,442. Its county seat is New Martinsville. The county, founded in 1846, is named for Lewis Wetzel, a famous frontiersman and Indian fighter. Its northern border aligns with the Mason-Dixon line, but is to the west of the line's western terminus.

The Mason–Dixon line, also called the Mason and Dixon line or Mason's and Dixon's line, is a demarcation line separating four U.S. states, constituting parts of the borders of Pennsylvania, Maryland, Delaware, and West Virginia. It was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon as part of the resolution of a border dispute involving Maryland, Pennsylvania, and Delaware in the colonial United States. The dispute had its origins almost a century earlier in the somewhat confusing proprietary grants by King Charles I to Lord Baltimore (Maryland), and by his son King Charles II to William Penn.