In the last year or so I've gotten my hands on another collection of local death letters. Here are two Allen ones that I didn't have previously-
Died. At his residence, Coole, Castleroe, On Monday, 7th July 1924, John Allen, Aged 75 years. The remains of my beloved husband will be removed for interment in Englishtown Burying-ground, on Wednesday, 9th inst., at Three o'clock (Summer Times). Helen Allen, Coole, Castleroe, 7th July 1924Died, At his father's residence, Glenleary, On Wednesday, 29th April, 1910, John Lawson, Fourth son of James Allen, Aged 7 1/2 years. His remains will be removed for interment in Camus Burying Ground, on Friday 22nd inst., at the hour of three o'clock, p.m. James AllenFor finding townlands, parishes, etc.- will also list adjoining townlands-
Glenleary-
https://www.townlands.ie/londonderry/coleraine/macosquin/somerset/glenleary/Camus-
https://www.townlands.ie/londonderry/coleraine/macosquin/somerset/camus/Note: couldn't get into site now but just keep trying.
This site for Griffith's Valuation will give details of individual properties- you can search by name or townland-
https://www.askaboutireland.ie/griffith-valuation/The maps are also useful for showing properties.
From the printed version of Griffith's Valuation (c1859 in this area) the Valuation Revision Books will continue details until almost 1930-
https://www.nidirect.gov.uk/information-and-services/search-archives-online/valuation-revision-booksIrish Genealogy is the place to find vital records (births, deaths, marriages) but most of the church records you need to check are not online. Some, but not all, have been microfilmed by PRONI in Belfast and Coleraine Libraries has copies of those microfilms.
In addition to the above sites, and others online, I have a large collection which includes many church records, gravestone inscriptions, death letters, landlords' records, school registers and family notes.