Although the Catholic parish of Kilbeagh is entirely within County Mayo, it appears that a part of the civil parish of Kilbeagh is across the border in Roscommon, and Currinah appears to be in that bit of the civil parish. You can see morre info about Currinah here:
If you move around the little interactive map at that site, you can see that Currinah is just down the road to the east of the town of Charlestown, which is in Mayo. The boundaries of the counties (and civil parishes) have changed from time to time over the years, and I seem to recall someone here (probably Roger McDonnell) mentioning boundary changes in the 1800's in that area where Mayo and Roscommon border one another.
That link has further links to records in Griffith's Valuation and the 1901 and 1911 censuses, and I see that you're right that Currinah is not found in Griffith's Valuation (or the link may be broken), although it is found in the 1901 census (but not the 1911 census). There were also changes over time in what was considered a townland, and it may be that Currinah was more of a "sub-townland" in the past (a local name for an area, not used officially), though it seems to be recognized now. The site also has links to info on the neighboring townlands, and perhaps what is now Currinah was in the past considered part of one of those townlands. However, their links to Griffith's Valuation are also not working, and the message is not the usual one, but instead an error message saying that the page cannot be found, which is why I said that there may be a broken link to the Griffith's Valuation records.
You may already know this, but the Catholic parish records for Kilbeagh (going back to 1845 for marriages, and 1855 for baptisms) can be found at this link: