Hi, This is the kind of thing that TalkIrish excels at, so I'm glad to say we can help you out here! The song is quite famous. It is called Cill Aodáin and it was written by Antoine Ó Raifteiri, or Raftery the Poet as he's sometimes known in English.
These are the words of Cill Aodáin:
Anois teacht an earraigh
beidh an lá ag dul chun síneadh,
Is tar éis na féil Bríde
ardóidh mé mo sheol.
Ó chuir mé i mo cheann é
ní chónóidh me choíche
Go seasfaidh mé síos
i lár Chontae Mhaigh Eo.
I gClár Chlainne Mhuiris
A bheas mé an chéad oíche,
Is i mBalla taobh thíos de
A thosóidh mé ag ól.
Go Coillte Mách rachaidh
Go ndéanfadh cuairt mhíosa ann
I bhfogas dhá mhíle
Do Bhéal an Átha Mhóir
Here's a rough English version:
Now's the coming of spring
the day will be lengthening,
And after St Brigid's day
I will raise my sail.
Since I thought of it
I will not stop at all
Until I will stand down
in the middle of County Mayo.
In Claremorris
I will be the first night,
And in Balla beside it
I will begin to drink.
To Kiltimagh I will go
To stay for a month,
Near enough two miles
From Ballinamore.
This may not be completely accurate but it's near enough. It's not exactly the same version on the Wiki article about Raftery but I think it makes more sense. I can't find a YouTube version (it's a really nice tune) but you should be able to find a version of it on Amazon - there's one by Gearóidín Bhreathnach which will cost you about a dollar to download!
Hope this is what you're looking for (I think it must be). All the best!