Looking for information adout Toohills

I think the parish mentioned in the letter could be Kilfinnane, which was based in the town of the same name in South Co. Limerick. RC baptism & marriage records for the parish go back to about 1832 - see : this map of RC parishes, and details of records for Kilfinane RC Parish (Irish Times). 

just spotted a Maurice Hogan listed in 1839 Catholic directory as the P.P. in Croagh parish. Post town for the parish is Rathkeale so further west in Co. Limerick -  he could have moved parish though sometime after that letter. Is the letter dated ?

checked into Maurice Hogan and he was P.P. in Croagh RC parish from the 1830s up to at least the late 1840s, so checked into that parish a little more, and discovered that one of the Civil Parishes covered by Croagh was named Kilfinny, so think maybe that's what the reference in the letter meant. See  the entry for Croagh on Lewis 1837 here (last paragraph refers to the RC parish layout)

The town of Croagh (village back in the 1830s), is located abt 5km east of Rathkeale, and you can see the village and the location of the RC chapel  from around that time on the 1st edition OSI maps Croagh village & Chapel (map is c1837). Kilfinny civil parish is to the south east of Croagh, and also had a chapel - see here , part of the same RC parish, so probably a chapel of ease for Croagh RC Parish.

Is dont see any town or townland that looks like a good match for Ballyfern either, but would definitely go along with your theory re Ballyfoleen as a likely match. There are two townland of that name in Kilfinny civil parish Ballyfoleen  North and Ballyfoleen South - see : here

The two townlands are listed on Griffith's Valuation as 'Ballyfoleon' north and south and dated 1852, but no sign of any Toohill, Carroll or similar households at that time. The Tithe records shows just 'Ballyfolin', and are dated abt 1834, and include a Patt and Danl. Touhill - I'd say these could be relations, probably Daniel snr (c1807) ... see : here  (National Archives). I'll confirm that date as the transcripts sometimes pick up the details from the parish entries before by mistake.

The townlands of Ballyfoleen  North and South are shown on the 1st Edition OSI maps, which are dated c1837 - see :   (the townland borders are shown in red ) You can see on the map that Ballyfoleen North townlands is adjacent to the village of Kilfinny, where one of the RC chapels was located.

Just to confirm the details for that Tithe entry for Kilfinny civil parish - the calculations are signed by a Henry Shaw, with a date of 16th September 1834.

Patt. & Danl. are listed together, with several plots of land - see entry 12, about 2/3rd down the page : Touhill, Ballyfolin townland