[2] Willis' appointment in Donegal antagonised the local Gaelic lords the O'Donnells who had traditionally enjoyed a close relationship with the Crown.
According to a 1614 history of Donegal Abbey written in Louvain, "The entire principality was plundered by Fitzwilliam's sheriff's and captains, to whom he sold the appointments.
One Boen, for example, obtained a captaincy for a bribe of two gold chains, which he gave to the sordid deputy's wife; and another, named Willis, got a similar preferment for sixty pounds.
As for our friars, they were obliged to betake themselves, with muniments and altar-plate, to the fastness of the mountains, to avoid Willis and his brigands; who a few months before Hugh Roe's return, swooped down upon Donegal in the dead of night, killing thirty of its inhabitants, and occupying the monastery as a garrison.
[4][5] Captain Humphrey Willis was killed in action in Ulster in 1602, a report to the Lord Deputy and Council & to the English Privy Council dated 14 July 1602 recorded the deaths of Sir John Barkley and Captain Willis during a campaign led by Lord Mountjoy against Tyrone in Monaghan "to push him from the plains into the fastness where he now is."