默瑟縣 (密蘇里州)

{{Infobox U.S. county
| state = Missouri
| county = Mercer County
| county_zh = 默瑟縣
| seal =
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| founded =
| named for =
| seat = Princeton
| largest city =
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| area_total_km2 = 1,179 km² (455 mi²)
| area_total_sq_mi =
| area_land_km2 = 1,176 km² (454 mi²)
| area_land_sq_mi =
| area_water_km2 = 3 km² (1 mi²)
| area_water_sq_mi =
| area percentage = 0.22%
| census yr = 2000
| census estimate yr =
| pop = 3,757
| population_density_km2 = 3
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| coordinates = {{coord|{}|0|N|{}|0|W|type:adm2nd|display=title,inline}}
}}
默瑟縣（）是美國密蘇里州北部的一個縣，北界。面積1,179平方公里。根據美國2000年人口普查，共有人口3,757人。縣治普林斯頓 (Missouri)。

成立於1845年2月14日。縣名紀念紀念在美國獨立戰爭的將領、代表馬里蘭州的眾議員約翰·F·默瑟 (John Francis Mercer)。