Succeeded the business of Goulding, Willis & Co. (c. 1814–17) at 7 Westmoreland Street but Goulding's music publications continued to be advertised as 'to be had at 7 Westmoreland St., Dublin' until c. 1826 (Boydell, 'Flageolet').

Advertised in the Faulker's Journal that the Musical Circulation Library contained 'upwards of twenty thousand musical publications' in 1820 (cited in Kerry).

Lawrence credits I. Willis & Co. for the sale of Spanish guitars in Ireland 'as early as 1824'.

Mark: 'Isaac Willis & Co., London' and 'Willis & Co.'

Succeeded in business by Robinson, Bussell & Robinson.

[Dates and addresses differ according to sources: the Dublin Directories give 7 Westmoreland Street from 1817 to 1819 and the Royal Harmonic Saloon, Musical Circulation Library from 1820 to 1836. Hogan gives 7 Westmoreland Street from c. 1816 to 1836. Waterhouse states that Willis fl from 1816 to 1836 at the Royal Harmonic Saloon, 6 Westmoreland Street. Boydell ('Flageolet') gives 7 Westmoreland Street from 1816/17 to 1837. Boydell (Card Index) gives 4 Westmoreland Street in 1836. Lawrence (citing the May publication) gives I. Willis & Co. at the Royal Musical Repository, 55 St James's Str. and 7 Westmoreland Street, Dublin c.1830. Note: Marcus Moses is listed in the Dublin Directories at the 4 Westmoreland Street address from 1831 to 1860. McHale states, in reference to Willis' pirated edition of Bunting's The Ancient Music of Ireland, that it was published c. 1800 but there is no evidence that Willis was in business either on his own or with Goulding at this date.]