The Duchy of Brabant was formed in 1183 as a state of the Roman Empire. It was divided between Belgium and the Netherlands with Antwerp and Brussels as its main cities. In 1830 there was a revolt against the Dutch rule. This resulted in the Duchy of Brabant gaining Belgian Independence.
The Grand Duchy of Moscow.
A barony is within a county or duchy. I suppose it would be possible for a barony not to be so, but I have never heard of it.
To rule a duchy, one must typically hold the title of duke or duchess, which is often inherited or granted by a higher authority, such as a king or queen. A ruler should possess leadership skills, political acumen, and the ability to manage the duchy's affairs effectively, including its economy and relations with other territories. Additionally, a strong understanding of local customs and the ability to garner the loyalty of subjects are essential for maintaining stability and authority.
Since the first duke of England was the Duke of Cornwall, the son of Edward III, 1337, I'm going to assume that the first Duchy would be the same, Duchy of Cornwall. The Duchy of Lancaster is held by the Soverign. in Lancaster the toast, "To the Queen, Duke of Lancaster" that's "Duke" not Duchess.
A duchy
Duchy of Urbino ended in 1625.
Duchy of Urbino was created in 1443.
Duchy of Carniola ended in 1918.
Duchy of Carniola was created in 1364.
Duchy of Friuli ended in 828.
Duchy of Friuli was created in 569.