Moson (Hungarian, German: Wieselburg) was an administrative county (comitatus) of the Kingdom of Hungary in present-day eastern Austria and northwestern Hungary, on the right (south) side of the Danube river. Moson is also the name of a town, nowadays part of the city Mosonmagyaróvár, Hungary.
Moson county shared borders with the Austrian land Lower Austria and the Hungarian counties Pozsony (Bratislava), Győr and Sopron. The river Danube runs along the north of the county, and the lake Neusiedler See lies partly in the county. Its area was 2013 km² around 1910.
The capital of the county was the town of Moson initially. The capital was moved to nearby Magyaróvár in the Middle Ages. Moson and Magyaróvár merged in 1939 to form the city of Mosonmagyaróvár.
The Moson comitatus arose as one of the first comitati of the Kingdom of Hungary.
In 1918 (confirmed by the Treaty of Trianon 1920), a tiny part of Moson county close to Bratislava became part of newly formed Czechoslovakia. The eastern part stayed in Hungary and merged with Győr county and a very small part of Pozsony county to form Győr-Moson-Pozsony county. The western part became part of the new Austrian land Burgenland.