spiregrain
It seems there are two sites, this one, which was sometimes just called Portora (if I remember right), and one at Cooper Crescent.

According to the Dept of Education (search here http://apps.education-ni.gov.uk/appinstitutes/default.aspx )- "A new school, Enniskillen Royal Grammar School (Ref: 242-0320) will open with effect from 1 September 2016. The school will initially operate on the 2 existing sites of Portora and the Collegiate. Portora Royal GS – 242-0042 and Collegiate GS, Enniskillen – 241-0040 amalgamated to form the new school. Postcode changed from 7HA to 5HD on 24/4/18 as per request from ETI"