The civil government of Cornwall was vested in the Duchy by the first of the Duchy Charters in 1337: A Charter of 1337 taken from the UK Statute Law Database
In fact, the first thing to be enumerated - being inter alia, annexed and united to the Duchy for ever - is the civil administration of the territory of Cornwall.
Therefore we have given and Granted for Us and our Heirs and by this our present Charter Confirmed to our same son under the name and Honor of the Duke of the said place: the Castles Manors Lands and Tenements and other things underwritten that he may be able to preserve the State and Honor of the said Duke according to the nobility of his kind and more easily support the charges in this behalf incumbent to wit the Shrievalty of Cornwall with the Appurtenances so that the aforesaid Duke and other Dukes of the same place for the time being at their pleasure make and constitute and may make and constitute a Sheriff of the aforesaid County of Cornwall to exercise and perform the Office of Sheriff there as hitherto it hath been accustomed to be done without the let or impediment of Us or our Heirs for ever
A County at that time was the territory presided over by an Earl/Count and rendered in Latin as 'comitatus', this is what has been translated above into 'county'. Within this there was a vice-comitatus (or Shrievalty) under the jurisdiction of the sheriff but who was normally the principal officer of the King of England. Within Cornwall, however, he was, actually, the principal officer of the Earls (and, later, the Dukes) as the above extract shows.
As with all things related to the creation of the English and then later British state such terms became ambiguous (leading to various Imperial half-truths) and eventually the territorially equivalent terms of comitatus and vicecomitatus became reduced, and rationalised, to 'county' as we understand administrative counties today. At no point however have the powers of the Duke over the civil administration of Cornwall been removed. As can been seen above this Duchy charter of 1337 is part of UK statute law, and it has on numerous occasions been reconfirmed by other acts of parliament also to be found on the statute law database.
The Duchy of Cornwall Management Act 1863 (c.49)
The Words “Possessions of the Duchy of Cornwall,” and the Word “Possessions” applied to the Duchy of Cornwall, shall include Regalities, Hundreds, Castles, Honours, Lordships, Manors, Advowsons, Forests, Chases, Woods, Parks, Messuages, Lands, Buildings, Rights of Common, Mines, Minerals, Rights of Entry, or other Rights in respect of Mines or Minerals, Rentcharges in lieu of Tithes, Fixtures, Services, Rents, Pensions, Annuities, annual Sums reserved on any Sale, Disposal, or Enfranchisement made under the Powers of this Act, Rights, Privileges, Easements, Possessions, Tenements, and Hereditaments whatsoever, whether in possession or reversion, Parcel or reputed or claimed to be Parcel of the Duchy of Cornwall, or annexed to the same.
The 1863 act being reconfirmed by the Tamar Bridge Act 1998
(1) Nothing in this Act affects prejudicially any estate, right, power, privilege, authority or exemption of the Crown including (without prejudice to the general law concerning the applicability of statutes to the Duchy of Cornwall) the Duchy of Cornwall and, in particular and without prejudice to the generality of the foregoing, nothing in this Act authorises the Authorities to take, use, enter upon or in any manner interfere with any land or hereditaments or any rights of whatsoever description......
......belonging to the Duchy of Cornwall or enjoyed by the possessor for the time being of the Duchy of Cornwall, without the consent of the Duke of Cornwall testified in writing under the seal of the said Duchy or, as the case may be, the consent in writing of two or more of such of the regular officers of the said Duchy or of such other persons as may be authorised under section 39 of the M1 Duchy of Cornwall Management Act 1863......
De Jure our Cornish administration (the civil government of Cornwall) is legally and constitutionally within the Duchy of Cornwall and not England even if 'de facto' this is clearly not the case.
So when did this change? When did the civil government of Cornwall get handed over to Westminster and what acts of parliament support this blatant alienation from the Duchy of Cornwall? With what mandate were these changes to the civil government of our territory made? Where the Cornish consulted?
On the TGG site under "Territory and People" and "County?" you will find a letter sent to the Duchy back in 1997, which sets out the questions that need to be answered within a constitutional context. The response was predictably useless.
Two forum threads on this topic: Cornwall 24 and This is NOT England.