Hi
Re your search for O'Connell.I did a search of the 1901 census and found a Thomas O'Connell (farmer) in the Townland of Magheranore : Parish of Achonry : Barony of Leyny : Co.Sligo
One of the sons is named Denis aged 9 years . This is a long shot but as some names are carried on in families this may be worth investigating. I estimate that this Thomas was married circa 1883. The marriage details of Thomas may help.This Thomas could be a brother to the Denis you are researching ?
A search of the 1911 census for the same area shows the family living in the same area and living with them is Anne Healy: sister- in - Law.
A search of Griffith Valuation for Magheranore Parish of Achonry Barony of Leyny shows 2 Healy holdings, But no O'Connell. A search of both Griffith and Tithe have no Thomas O'Connell
Magheranore is in South Co. Sligo . The townland is on the R294 Tubbercurry (Tobercurry to Ballymote/Gurteen Road

http://www.sligococo.ie/library/maps/1837/index/parishTownla...
You will also find this place on Google maps.
Because Magheranore is so close to the Mayo border it may be that Thomas came into this area from another county
Best of Luck
Rosaleen