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 Żagań was created in 1274.
Duchy of Bytom ended in 1498.
Duchy of Friedland was created in 1627.
Duchy of Burgundy was created in 843.
Duchy of Burgundy ended in 1477.
Duchy of Carinthia was created in 976.
Duchy of Carinthia ended in 1919.
Duchy of Carniola ended in 1918.
Duchy of Carniola was created in 1364.
Duchy of Florence was created in 1532.
Duchy of Florence ended in 1569.