It is the principal post office of Dublin and is situated in the centre of O’Connell Street, the city’s main thoroughfare. It took 3 years to build beginning 1814 and on the 6th January 1818, the new post-office in Sackville Street (now O’Connell Street) was opened for business.
https://www.castle-hotel.ie/directory-entry/general-post-office-g.p.o.



