A duchy is the jurisdiction of a Duke. You'd have to check out the specific duchy for more detailed information. A good place to start is the British Royalty website.
Duchy of Savoy ended in 1713.
United Baltic Duchy ended in 1918.
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 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.
duchy
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.
Duchy of Florence was created in 1532.
Duchy of Florence ended in 1569.
Duchy of Württemberg ended in 1806.
Duchy of Württemberg was created in 1495.
Duchy of Żagań was created in 1274.