Looking for parents of John Lynch

I am hoping someone may have some constructive/instructive advice on my continued search for the parents of my GGG-Grandfather, John Lynch. What I know is, he was born about 1815 (various records show his birth to be from 1815-1817). Originally, I only knew from his US Civil War enlistment record, that he listed Co. Cork, Ireland as his place of birth. All other, US records simply show his place of birth as Ireland. I have tried to locate Naturalization paperwork that I can definitively tie to him and have been unsuccessful in the courthouses in the area he resided. There have been a few John Lynch's on ship manifests that have potential to be my John but no way to know for sure which one it might be or if any of them are him. Having run into this brick wall at the shores of the US, trying to get evidence of John Lynch on Irish soil and to find out who my 4X Great Grandmparents are has proven daunting.

I have since turned to DNA in the hopes that I might find an Irish match that has a tree that might help find the link. In the last 5 years, that has not happened, however, through the DNA, pouring over and analyzing what trees are available from matches, I have been able to reasonable identify where in Co. Cork I believe John may have been born. It would appear that John was from the Ballyvourney area of Co. Cork, possibly even Macroom area. The names that seem to be associated the most with my matches for that line are, Kelleher, Lucey, Buckley, Cronin, Twomey and to a lesser degree, O'Donoghue, McSweeney, McCarthy.

Naming sequence has not helped identify a particular family unfortunately. John's first child was a boy named Daniel, however, his wife's father's name was Daniel and there is not any way to know if Daniel was also John's father's name, since there is no record. After Daniel the names follow, Olive, Clay, Levi, Clinton and Mary. These are children from his first wife. From his second are all daughters, Sally (believed to be named after the first wife), Matilda, Eliza and Jane.

I have tried to use various Irish websites to look up records, however, the difficulty I find is, IF if  I find a potential record, I then run into the problem of how to tie my John to that record. There were many John Lynch's born in Co. Cork and also in Co. Kerry, where a few matches have had information in their trees that suggest possibly the Kenmare or Kilgarvin area of Co. Kerry. That said the big prevalance in trees is the Ballyvourney/Macroom area. Most of my matches trees do not go back to the 1815 time period, they seem to stop right around 1830, so obviously, quite frustrating.

Last of all, I did have a genetic genealogist look over my work and although she would not go out on a limb and say 100% John came from Ballyvourney or Macroom, she did say the evidence strongly suggests this to be the case. To round out my information about John Lynch, he settled in Edwardsville, Illinois, was married twice. First to Sally Ann Lanterman in 1842 and then after her death in 1852, he married Eudoxia Ann Scott in 1853. He enlisted in the Civil War at the start and was discharged in ill health in 1864 outside of Richmond, Virginia. The Company Dr. told him not to return to Illinois due to the cold weather and to stay in the south. He died in March of 1866 in New Orleands, Louisiana, having never made it back home to Edwardsville.

Again, any constructive or instructive advice or help would be greatly appreciated. Thank you so much for your time reading this.