The County of Guastalla was a feudal state in northern Italy, centered on Guastalla. The title of count was created in 1406 for Guido Torelli.
The Torelli family ruled Guastalla until 1539 when it was purchased by Ferrante Gonzaga. Another branch of the Torelli family held the County of Montechiarugolo, which was created in 1456 from a split in the County of Guastalla, until 1612.
Ferrante Gonzaga's descendants ruled Guastalla until 1746, being raised to the title of duke in 1621 when the territory became the Duchy of Guastalla. The last Gonzaga duke, Giuseppe Gonzaga, died heirless in 1746, at which point the territory was briefly incorporated into Austrian Lombardy.
With the Treaty of Aix-la-Chapelle in 1748, Guastalla was ceded to the Duke of Parma.