There are many sites relating much the same information about the origin of the Keogh name and the earlier history of the Keoghs.
KEOGH
Keogh, and its variant Kehoe, are the anglicisations of the Irish Mac
Eochaidh, from eoch, meaning ‘horse’. It arose as a surname in three
distinct areas. The first was in south Roscommon, around Moyfinn in the
barony of Athlone, which used to be known as ‘Keogh’s country’. This
family was part of the Ui Mhaine tribal grouping. The second was in west
Tipperary, near Limerick city; the placename Ballymackeogh marks the
centre of their territory. The third and most important, both
numerically and historically, was in Leinster, where the original
homeland was in north Kildare, whence they migrated first to Wicklow and
then south to Wexford. It is in Wexford that the name has been most
commonly anglicised Kehoe. The surname is now most frequent in Leinster,
though it has become widespread throughout Ireland.
http://homepage.eircom.net/~kthomas/names7.htm
www.surnamedb.com/surname.aspx?name=Keogh
http://www.houseofnames.com/xq/asp.fc/qx/keogh-family-crest.htm
Map of parishes in County Sligo (cached)
Kilmacallane - Entry from Lewis's Topographical Dictionary 1837 (cached)
Keoghville - seat of the Keoghs of Roscommon (cached)
Mary O'Brien, daughter of Cornelius O'Brien, married
Cornelius Keogh, great-grandson of
John Keogh. The following links provide information on Cornelius
O'Brien.
http://www.burrenpage.com/corneyobrien.html
http://www.clarelibrary.ie/eolas/coclare/people/cornelius_obrien/cornelius_obrien.htm
A well known Keogh in the USA is Myles Keogh, killed
in 'Custer's last stand'. He is not known to be related to
John Keogh but the link is included for interest.
http://indigo.ie/~wildgees/keogh.htm
Far more detail on
http://www.myleskeogh.org
Griffith's valuation of Ireland was a survey carried out between 1847 to 1865 to assess liability for poor rates. For more information see http://www.from-ireland.net/gene/griffithsval.htm
For access to the source data see Griffith's Valuation