Shinrone and Birr will meet in the other semi-final this weekend.
St Cillians have booked their place in the final of the Offaly Senior A Camogie Championship.
They produced a strong second half performance as they defeated Tullamore on a scoreline of 1-16 to 0-12.
They will face the winners of the other semi-final between Shinrone and Birr, which takes place this Saturday.
In the Senior B, Kilcormac-Killoughey had a 2-11 to 1-07 win over Naomh Brid, while St Rynaghs hammered St Sinchills 4-20 to 1-01, as they both booked their places in the decider.