As of Sept 1st 2017, the Irish Naturalization and Immigration Service have reverted the co-habitation requirement from 1 year to a minimum of 2 years. They had temporarily made this change in 2017, but as of now, you will need to prove 2 years of living together.

This will effect the partners of Irish citizens who want to return to live in Ireland with them. If this describes you, then I strongly advise you read the information at the following link:

http://www.inis.gov.ie/en/INIS/Pages/De+Facto+Relationships