Ballynagall, at Knockdrin, Co. Westmeath, is adjacent to Lough Owel and was the Demesne of an estate mansion. A small section of it is located in the civil parish of Portnashangan / Tyfarnham (where your Robert Dagg is recorded as having land), However, the Ballynagall Demesne was largely in the civil parish of Rathconnell. So it may be helpful in the future for you to to join the Rathconnell Community on IrelandXO as well! Mullingar (just south-east) was this Ballynagall's nearest market town (which generally was the address given on ships' manifests).
Your ancestors lived on the demesne of Ballynagall House, Knockdrin which at that time was the seat of James W. Middleton Berry Esq. This gentleman was an extensive proprietor of estates in Co. Meath, Co. Westmeath and King's County (now Co. Offaly) and Deputy Lieutenant of Co. Westmeath in 1855.
The handsome Grecian mansion of Ballynagall had long been the seat of the Gibbins family. In 1846, through the will of James Gibbons Esq. its ownership passed to a James W. Midleton Berry Esq. of Middleton, Co. Westmeath, who married Caroline Augusta Smith (d.1896), daughter of the Right Hon. TBC Smith, Master of the Rolls in Ireland in 1851. Mr Middleton Berry resided there until his sudden death at a hunt in December 1855. (Interred at the family vault at Ballynegall Church). Ownership of Ballynagall then transferred to his in-laws, the Smyth Family.
You can find Ballynagall here on Griffith's Valuation, which gives you a snapshot of 1855. The record shows the larger townland of Ballynagall (Rathconnell) comprised of "gate lodges and land" held in fee (owned) by James W.M. Berry Esq. of Ballynagall House, landlord (who also appeard in Griffith's as Jas. William M. Berry). The smaller townland of Ballynagall (Portnashangan) was right beside Ballynagall Church and Glebe House/ Rectory.
Robert David Dagg held a whopping 91 acres on the Ballynagall Demesne. He had to have been an employee of Mr Middleton Berry, most likely an agent or steward. (That the names of the occupants of these gate lodges were not recorded in 1855 does not suggest they were unoccupied).
The timing of Robert Dagg's short tenure in Ballynagall would appear to be very much connected to this James William Middleton Berry Esq. of Ballynagall (d.1855). Berry came into possession in 1848; Dagg was in a good position to marry in Portnashangan parish in 1849. Berry's sudden death at the end of 1855, led to the quick sale of his hunting horses in January 1856, and his widow auctioned all carriages, horses, stock, crops and farm implements at Ballynagall in April 1856. Robert Dagg emigrated in 1856.
It certainly looks like Robert David Dagg was invited to Ballynagall as a trusted employee of Middleton Berry. Upon Berry's sudden death, Dagg was out of a job and emigrated (why else would he have given up 91 acres of good land?).
Should the Middleton-Berry or Smyth of Ballynagall landed estate records survive (try the NAI and the NLI), you have a good chance of finding out more. Getting to know the extent of this Middleton-Berry estate will help narrow down your possible point of origin.
Best of luck!
