The formal agreement between The Hononorable the Irish Society and Londonderry Corporation by which the former agreed to provide a site for a new Town Hall to replace the by then inadequate civic building in the centre of the Diamond was entered into on 28th April 1886. In addition to agreeing to grant the Corporation the necessary land for what was to be known as the Guildhall the Irish Society also agreed to provide funding up to the sum of sixteen thousand pounds to include all expenses and the costs of fitting out.
It was a term of the agreement that the Irish Society should see and approve any tender for the construction works before it was formally accepted by the Corporation. It was further agreed that once the building was completed and furnished and possession had been taken by the Corporation that at that stage the Irish Society would grant the Corporation a lease in perpetuity, (a fee farm grant), of the site reserving an annual ground rent of £400. It was stipulated that the deed would contain a covenant to the affect that the land and buildings could not be used for any purpose save for the purposes of, "a Town Hall, Corporation Offices and other similar purposes for which Town Halls and the buildings erected therewith are commonly used." For some years prior to 1886 the Irish Society had been making an annual allowance of £1283 for certain specific purposes. The Fee Farm Grant was to include a clause stating that if the annual fee farm rental of £400 was not paid by the Corporation that the Irish Society could retain the said sum from the monies paid by way of the annual allowance. The Fee Farm Grant to the Corporation was ultimately dated 6th July 1892.
Some six years later by way of a deed dated 28th June 1898 the Irish Society conveyed the rental to the Corporation, the Corporation having agreed to forego an annual allowance of £400 which the Irish Society was to give the Corporation for ten years to assist with the Killea water supply. The restrictive covenant as to use contained in the Fee Farm Grant was reaffirmed in the 1898 assurance.