Simon Campbell

Statutory birth, death and marriage registration (in some jurisdictions called Vital Records) only started in Ireland in 1864, save for non RC marriages which were recorded from 1845 onwards. So you won’t find statutory birth, death or marriage certificates in Ireland for this family. For earlier years you usually need to rely on church records, where they exist. You obviously need to know the precise denomination in order to search the correct records. Not all churches have records for that period and not all are on-line.

RC records are mostly on-line on the nli site:  

https://www.nli.ie/en/family-history-introduction.aspx

For other denominations, the churches usually hold the originals but there are also copies in PRONI, the public record office, in Belfast. A personal visit is required to access them. Access to the records there is free. This link explains what records exist, parish by parish:

https://www.nidirect.gov.uk/publications/proni-guide-church-records

However if you don’t know where in Tyrone the family lived, then it’s a needle in a haystack. I searched the records for the Londonderry Sentinel to see if the marriage was published in the newspaper but did not find it. Campbell is a fairly common surname in Tyrone so that doesn’t help either. However Lennox is not so common. In Griffiths Valuation c 1860 there were just 2 households. One in the parish of Kildress and the other in Leckpatrick. So they might be the parishes to focus on.

I checked the 1901 census of Tyrone. There were just 3 Lennox households then. One was a teacher born in Monaghan and the other was a farmer from Scotland, so that left just one who was native to the area (though the name is obviously Scottish so they probably originated in Scotland too at some earlier period).

Claire,

Church of England in Canada is Church of Ireland, in Ireland.

The death record you have given is available on-line. Here it is:

https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1901/05719/4613705.pdf

Simon was a farmer in the townland of Radergan. That’s in the parish of Clogherny. Sadly their early Church of Ireland baptism records were destroyed in the 1922 fire in Dublin and they have nothing earlier than 1859 now. (Marriages from 1845). This is Simon in the 1901 census. Note that he was Roman Catholic. Does that fit with your information? Is it the right family?

http://www.census.nationalarchives.ie/pages/1901/Tyrone/Beragh/Radergan/1748751/

You may notice a bit of a difference between Simon's age in the census 90 (taken in April 1901) and his death a couple of months later (101). Most people then didn’t know their age and just guessed. Discrepancies like this are very common in Irish records.

The RC records for the parish (RC parish of Beragh) start in 1832. The RC parish records are on-line free on the National Library site:

https://www.nli.ie/en/family-history-introduction.aspx

The informant for the death was H. Owens, son in law, of Beragh. I suspect this is him in the 1901 census:

http://www.census.nationalarchives.ie/pages/1901/Tyrone/Beragh/Beragh_Town/1748812/

Simon’s probate abstract. The full will should be in PRONI. It isn’t on-line. You can pay them to copy it or you can view it free if you go yourself.

Administration (with the Will) of the estate of Simon Campbell late of Radergan County Tyrone Farmer who died 2 August 1901 granted at Londonderry to Henry Owens General Merchant.

There wasn’t a Campbell farm in Radergan in the tithes in 1828 so that suggests Simon acquired it after that year. He is listed there in Griffiths Valuation c 1860, along with a Thomas Campbell.