Kevin,
You ask where the 1948 date comes from. Thomas Tierney died in 1930 but there was a delay in getting probate (not uncommon) and it was 21.12.1948 before it was obtained, and granted to Arthur Tierney (who seems likely to have been his son). So that suggests Arthur was probably still farming there then. My information comes from the PRONI wills site:
https://apps.proni.gov.uk/WillsCalendar_IE/willsSearchResultsDetails.as…
That will should be in PRONI in paper format and you might find it helpful in tracing his descendants. (If you want a copy of it, PRONI will post or e-mail that to you for a fee. If you go in person you can view it free. The important date is the date probate was granted, rather than the date of death. The files are kept in date order of the grant date, not the death date)
This is presumably Thomas’s son Arthur in the 1911 census, aged 7:
http://www.census.nationalarchives.ie/pages/1911/Tyrone/Carryglass/Carryglass/871498/
I had a look in the current phone book for Trillick & postcode BT78 but did not see any Tierneys listed. However so many people are not listed these days that doesn’t mean much.
The death records for Northern Ireland are on-line up to 1968. I searched them up to that year but saw no sign of Arthur. So assuming he was still in Northern Ireland then, he must have died after 1968. I also looked for a marriage for him up to 1943 (which is as far as the on-line marriage records go) but did not find one.
To search for deaths and marriages after the years given, you need to go into PRONI or GRONI in Belfast as they have terminals there that allow you to search more recent events, right up to events registered yesterday. PRONI also has the wills for people who died after 1966. So you might find a will for Arthur as well as his date of death. The PRONI staff will explain how you do that.
You ask about tracing the family forward. That can be very difficult if you have no clues as to where they were living. And many of the records you might want are closed. I looked at Thomas’s children in the 1911 census. Apart from Arthur, there was James 16, Patrick 14, Mary Ellen 13, Catherine 9, Bridget 4 & Teresa 2. I didn’t check the death records. (You could do that on the GRONI site) but I did look for marriages for them. Carryglass is in the Omagh civil registration district. So I searched all Tierney marriages from 1916 to 1943 registered in Omagh. I found James Tierney’s marriage on 19.1.1920 to Mary Campbell:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_re…
There was also a Mary who married a Cooke on 10.1.1928. That’s not available on the irishgenealogy site. If you want you can look at that certificate on the GRONI site to see if it’s your family. It costs £2.50 (sterling) to view a certificate there. Otherwise I did not see any marriages for any of the other children. So chances are they scattered. They probably moved to Belfast, Dublin, Britain or further afield to find work, and then perhaps married there. Without some inside information from a will or someone alive today, it's nigh on impossible to trace them. The only exception might be the Tierney/Campbell marriage. It’s easy enough to search the birth records in PRONI to see if they had any children and from that you can track the family forward for a bit. Till they stopped having children anyway. But you have to go to PRONI or GRONI to search births within the past 100 years. They are not on-line anywhere else. And they cost £2.50 a time to view.
I would get a copy of Thomas’s will as it may give you a snapshot of where his children were in 1930. Plus if any of the girls have married you may get their married names which is always helpful.
I would also ask around at the farm and in the local area. If the farm is no longer in Tierney hands, neighbours may know where some of the family are now. And the parish office may be able to tell you of any Tierneys in their congregation. I wouldn’t be apprehensive about approaching possible members of the family in the area. Most people will be very friendly. Your problem may just be that they don’t know that much about their family. Irish people aren’t always that interested in their ancestry. (We generally know where our ancestors came from and don’t have that much curiosity about them, save perhaps for the odd notorious one. “Old uncle Liam who eloped with a duchess.” We remember that sort of thing.). So what you tend to find is that most folk can go back about 3 generations, to around 1900, and after that it all gets a bit hazy. And with common names, the families all tend to get hopelessly mixed up. When you are dealing with ancestors who left in the 1860s it can be tricky identifying the right family. There’s often a bit of a knowledge gap. You may find yourself knowing more about the family than the folk here do. And there’s unlikely to be a family bible with all the generations names. I’ve never seen one. Not in Ireland anyway.
1911 is the most recent census open to the public. The next was in 1926 but the bit for Northern Ireland has been lost. Also one in 1937 but it’s closed till 2037. There is the 1939 Register which was a summary of the population compiled at the outbreak of WW2 for conscription and ration book purposes. It isn’t on-line but can be accessed in PRONI if you make a Freedom of Information request. But it’s quite tedious system. If people are under 100 you need to show they are dead, before they’ll open the records, so all rather complicated. Especially if you don’t know if they are dead.
To find the Tierney farm in Carryglass, you need to go to Griffiths Valuation:
http://www.askaboutireland.ie/griffith-valuation/index.xml
Search under Griffiths Places and enter Carryglass and Tyrone. Then click on the map view option. This will bring up a map of the area around Carryglass compiled in the 1870s. If you enlarge it you should see Carryglass easily enough. The townland boundaries are outlined in red. Each plot has a number and some suffix letters. So 22 was the Tierney farm with 22a being James Tierney’s house and 22b Patrick’s. In the top right hand side of the screen there’s a slider bar that allows you to switch to a modern map. You should see from that, that the Tierney farm is up a lane near Sean Kelly Commercials. Their address is 93 Carryglass Rd, Trillick BT78 3PU. That’s off the Glengeen Rd. If you have a satnav it should get you there, and then you’ll need to do a bit of local navigation to complete the last bit up to the farm.
Street names and house numbers were only introduced in this part of Ireland in the 1960s, so I don’t know what the Tierney farm’s exact address is today. In the 1860s, your townland alone was enough to identify you. So a letter would have been addressed to “Patrick Tierney, Carryglass, Trillick” and would have got there. The postman knew where everyone lived and so no further detail was required. Now we have got a bit more detailed with our addresses, otherwise we don’t get our parcels from Amazon.
You should be able to look at the farm today on Google earth by searching under postcode BT78 3PU.