默瑟縣 (西維吉尼亞州)

{{Infobox U.S. county
| state = West Virginia
| county = Mercer County
| county_zh = 默瑟縣
| seal =
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| founded = 1837
| named for =
| seat = Princeton
| largest city =
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| area_total_km2 = 1,090 km² (421 mi²)
| area_total_sq_mi =
| area_land_km2 = 1,089 km² (420 mi²)
| area_land_sq_mi =
| area_water_km2 = 1 km² (0 mi²)
| area_water_sq_mi =
| area percentage = 0.06%
| census yr = 2000
| census estimate yr =
| pop = 62,980
| population_density_km2 = 58
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| coordinates = {{coord|{}|0|N|{}|0|W|type:adm2nd|display=title,inline}}
}}
默瑟縣（Mercer County, West Virginia）是美國西維吉尼亞州南部的一個縣，南鄰維吉尼亞州。面積1,090平方公里。根據美國2000年人口普查，共有人口62,980人。縣治普林斯頓 (Princeton)。

成立於1837年3月17日。本縣紀念在美國獨立戰爭普林斯頓戰役中戰死的休·默瑟准將 (Mercer County)。