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.
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 Racibórz was created in 1172.
Duchy of Silesia ended in 1918.
Duchy of Silesia was created in 1163.
Duchy of Westphalia was created in 1180.
Duchy of Bielsko was created in 1572.
Duchy of Głubczyce was created in 1172.
Duchy of Zator was created in 1454.