My wife Mary was born a Colby and famly traced to North East England (South Shields) family was then traced back to KILKENNY and no further details found
We made contact in US and AUSTRALIA who had also hit brick walls with research there
I am of the option that COLBYS may have come to IRELAND in 1700-1850 from North East to work in Mines there,
I remain hopefully to solving the riddle and welcoime ideas or leads.
According to this link, the surname is very rare in Ireland. In the mid 1800s there was just one household in Co Cork, one in KIlkenny and two in Mayo. The surname is not listed in the handbook of Irish surnames, which indicates it’s unlikely to be a native Irish name.
http://www.irishtimes.com/ancestor/surname/index.cfm?fuseaction=Go.&UserID=
There were only 3 Colby households in Ireland in the 1901 census. Two of them were born in England, just one born in Kilkenny. So probably an English surname but tracing back to the 1700s will be difficult if not impossible, I suspect.