[1] Oldham was a prominent member of the Statistical and Social Inquiry Society of Ireland, for whom he was Barrington Lecturer (1895 to 1901) and President from 1924 to 1926.
[2] In his Dictionary of Irish Biography entry, Oldham is described as a "Gladstonian liberal", but also holding strong Irish nationalist sympathies as an admirer of the writings of Young Irelander Thomas Osborne Davis.
[1] A close friend of Oldham was Irish separatist and Fenian John O'Leary.
[1] Oldham managed the southern (Dublin) branch of the Irish Protestant Home Rule Association which he had founded in 1886.
[1] Oldham was friends with analytical chemist Arthur Cranwill (treasurer of the Irish Protestant Home Rule Association), and encouraged his daughter, the future designer and metal artist Mia Cranwill to study Irish history and mythology during her visits to Dublin.