Jennifer,
The information you have about Watergrasshill may be a bit inaccurate. The nineteenth century records in Ireland are in Civil Parishes. Several Civil Parishes were amalgamated to form Church Parishes. Watergrasshill is a Church Parish and one of the Civil Parishes that makes up Watergrasshill Church Parish is Ardnageehy. Rathcormac Church Parish consists of Rathcormac Civil Parish. So the two parishes you are interested in are Ardnageehy and Rathcormac. Rathcormac is the next parish to Watergrasshill and I think Ann Jones was from Rathcormac. The Jones family seem to have lived close to the boundary of the two parishes. Generally speaking, a marriage took place in the bride’s home parish. Pierce and Ann were married in Rathcormac. Also, the parish given for the birth of Ann and her siblings was Rathcormac. Finally, the birth of Catherine O’Toole (the oldest child of Pierce and Ann) was registered in Rathcormac, although the residence of Ann and Pierce was given as Watergrasshill. In many cases, a woman went home to her parents house to have her first child.
The parents of Ann Jones were William Jones and Elizabeth Mullins. William and Elizabeth had 5 or 6 children: Henry (1808), Frances (1813), William (1814), Ann (1816) and James (1819). Richard Jones (1809) was registered in Rathcormac in 1809 with parents William Jones and Elizabeth Jones. It is easy to see how this could be an error.
As you say, Pierce and Ann were married in 1842. Their first child, Catherine, must have died as a subsequent child, born 12 years later, was also called Catherine. In 1842 they lived in Watergrasshill and in 1854 no address is given. When Christopher (1856) and Margaret (1863) were born the address given is Fermoy.
In the 1853 Griffith's Valuation Henry Jones held just over an acre in the townland of Behernagh, parish of Rathcormac. William Jones from Corbally (the next townland, but in Ardnageehy parish) died in 1892 aged 75. This could be William son of William and Elizabeth.
Also, in 1853, Patrick Toole had just over 6 acres in Meenane townland in Ardnageehy parish, a few kilnmetres from where the Jones family lived. This could be a father or brother of Pierce? There were very few O'Toole/Toole families in Cork at the time and the one on Ardnageehy fits best. As records in Watergrasshill (Ardnageehy) didn't begin until 1836, you are unlikely to get a record.
There is a cemetery in Ardnageehy, but there is only one reference to a headstone that may be of relevance. Katie Hickey (nee Twohill) died in 2004 aged 87. She was from Bridestown townland in the parish of Ardnageehy, which is just beside Berhanagh townland.
Maybe Pierce O'Toole/Toole/Twohill came from Ardnageehy Civil Parish, Watergrasshill Church Parish? Alot to digest! Get back to me for any clarifications or further information.
Best wishes, Kieran