Here's the onomasticon entry for 'ath ceit' (Cet's Ford) --
Hk. 384; ¶ seems in Connacht, or on borders of Connacht and Ulster"
I can't connect this to a modern placename.
"Ferdia's Ford (modern Ardee) marks the spot where Ferdia was killed by
Cuchulainn in the Táin, which makes me wonder if Cet's Ford will turn out to
be the place where Cet meets his death. Liz