Initially Davies brought over sixteen families and then set about rebuilding the castle. He finished it in 1610 but he did not possess the necessary engineering skill to build the tunnel under the river with which local folklore has accredited him. He did however add a bridge over the river a few years later.This bridge ( which 200 years later John Gamble found to be narrow and inconvenient) was so well built that it was only replaced in 1835. In addition Davies is credited with turning the existing collection of mud huts into something vaguely approaching the town of Castlederg as we know it today.
When he died in 1626 (having just bought his robes on a hint that he was to become Lord Chief Justice of England) the area passed to his daughter who married Lord Hastings. Known now as the Manor of Hastings, (at this time when a woman married her property came under the control of her husband), it was subsequently bought by Edward Edwards and eventually portions of it were acquired from his family either as settlement for debts or through marriage by the Ferguson and Smyly families. Ferguson Crescent and Edwards School are present-day reminders of these landlords.
In 1641,Phelim O'Neill,as part of his attempt to drive out these newcomers laid siege to Castlederg and managed, before being driven off,to inflict substantial damage to the castle. Local farmers seeking building material completed its destruction.
During the 1600's the Plantation of Ulster continued. In the Castlederg area this consisted of an influx of members of the Presbyterian faith from Scotland into the region around the town and the lower part of the Derg valley. Some at least of these had reservations about what was being offered. John Gamble (who had remarked on this "romantic little town"at the beginning) tells of one of his ancestors being offered a large tract of land by Sir John Davies. The next day however he had to refuse the offer telling Sir John that "my gude wife would not rest if she thought her bairns were living on land which had been taken over other people's heads"
Nevertheless the original inhabitants were moved to the higher and more desolate land round Ballymongan and the Corgaries. The descendants of both groups still make up much of the population of the area today.