Teach an Ard-Mhéara aka The Mansion House built in 1710, was purchased from Joshua Dawson in 1715 as a residence for the Lord Mayor. A rotundo (now the Round Room) was added in 1821.
Excerpt from Lewis' Topographical Dictionary of Ireland for the metropolis of Dublin in 1837:
"The Mansion-house, the residence of the lord mayor during his year of office, is externally a plain edifice of brick, on a detached and receding site on the south side of Dawson-street; the interior contains some large apartments fitted up in an antiquated style.
- On the left hand of the entrance hall is the "Gilt Room," a small apartment in which is a portrait of Wm. III., by Gubbins; this room opens into the drawing-room, which is 50 feet long: the walls are hung with portraits of Earl Whitworth, the Earls of Hardwicke and Westmoreland, John Foster, the last speaker of the Irish House of Commons, and Alderman Alexander.
- Beyond this is the ballroom, used also for civic dinners, 55 feet long and wainscoted with Irish oak; in this room are placed the two city swords, the mace, the cap of maintenance and the gold collar of S S, presented by Wm. III., to replace that presented by Chas. II. ; it also contains portraits of Chas. II., Geo. II., the Duke of Cumberland, and the late Duke of Richmond.
- A door from the ballroom opens into a noble rotundo, 90 feet in diameter, round which is continued a corridor 5 feet wide; the walls are painted in imitation of tapestry, and the room is covered with a dome; in the centre is a lantern, by which the apartment is lighted; it was built in 1821 expressly for the reception of George IV., who honoured the corporation with his presence at dinner.
- On the right of the entrance hall are the Exchequer-room, wainscoted with Irish oak, and hung with portraits of the Duke of Bolton, the Earl of Buckingham, the Marquess of Buckingham, and the Earl of Harcourt; and the sheriffs' room, 40 feet long, in which are portraits of the Duke of Northumberland, Lord Townsend, John Duke of Bedford, and Aldermen Sankey, Manders, and Thorpe, the last of whom is distinguished by the title of "the good lord mayor."
- An equestrian statue of Geo. I., which was formerly on Essex bridge, is placed in the lawn at the side of the mansion-house; and at the extremity of the court in which the rotundo is built are colossal statues of Chas. II. and Wm. III.
The City Assembly-house, purchased by the corporation from the artists of Dublin, by whom it was built for an exhibition-room, is a plain but commodious structure in William-street, and contains several good rooms; in the circular room the common council holds its meetings; the board of aldermen meets in another apartment, and under the common council room is a circular apartment in which the court of conscience is held."
Since 1841, the Oak Room has contained the coats of arms of all former lord mayors, commencing with Daniel O'Connell.
Over the years, the Corporation added external rendering, the fine porch and the round room adjacent, which was built for the visit of George IV, and was the venue for the first sitting of Dail Eireann in 1919.