The region with the lowest support right now is Roscommon-Galway, with 57.21% - 42.79% for Yes. In 2015, it was the only region to vote against Gay Marriage.
Mayo came in just now at 57.07% Yes, so slightly less than Roscommon-Galway. Still possible that Donegal, Sligo-Leitrim or Cavan-Monaghan could be stronger for No than Mayo (I could even see Donegal actually voting No).
Also, the constituencies have changed since the same-sex marriage referendum. Results in the former Roscommon-South Leitrim are not directly translatable to the current Roscommon-Galway (especially since Leitrim is a more socially conservative area than Galway).
Dun Laoghaire at 77.06% Yes is the strongest Yes thus far, narrowly ahead of Dublin Fingal at 76.96% Yes; the only possible remaining constituency that could beat it is Dublin Bay South.