Mszczonów County (Polish: powiat mszczonowski) refers to a former administrative unit (powiat) in central Poland, with its seat in the town of Mszczonów. It existed during two distinct periods in the 20th century.
First Existence (1919–1939) The county was established in 1919 within the Warsaw Voivodeship of the Second Polish Republic. It functioned until the invasion of Poland in September 1939.
Second Existence (1952–1975) The county was re-established in 1952 within the Warsaw Voivodeship of the Polish People's Republic. It was abolished on June 1, 1975, as a result of the administrative reform that replaced the three-tier system (voivodeship, county, commune) with a two-tier system (49 smaller voivodeships, communes).
Subsequent Administration Following the 1975 reform, the territory of the former Mszczonów County was incorporated into the newly created Skierniewice Voivodeship (1975–1998). After the 1999 administrative reform, which reintroduced counties (powiats), the area became part of Żyrardów County in the Masovian Voivodeship.
