I've a bit of an amateur interest in the decline of Irish in Ulster. As far as I know there was Irish in Tyrone up until
1950, and certainly in the 1900s. However it was mostly concentrated in the north of county. Garrett Fitzgerald's
(which give projections on the number of Irish speakers based on the 1901 census) maps give only 3-10% of the
population as Irish speaking for the Tyrone-Monaghan border in the 1850s.
Guth in Eag, a programme about Irish in Tyrone, has some good information. Although from the wrong area of the county:
http://www.youtube.com/watch?v=h5cvPskVm3YCoiscéim is currently producing a series of books on words gathered from the dialects which are no longer with us.
The first in the series is about the dialect of Oirialla. I believe there are ones planned for the dialect that encompassed Tyrone, Fermanagh and Northern Monaghan.
I'll see if I can find out more.