The Indian National Congress conducted its first session in Bombay from 28 to 31 December 1885 at the initiative of retired Civil Service officer Allan Octavian Hume, known for his pro-Indian activities. In 1883, Hume had outlined his idea for a body representing Indian interests in an open letter to graduates of the University of Calcutta. It aimed to obtain a greater share in government for educated Indians and to create a platform for civic and political dialogue between them and the British Raj. Hume took the initiative, and in March 1885 a notice convening the first meeting of the Indian National Union to be held in Poona the following December was issued. However due to a cholera outbreak there, it was moved to Bombay.
From the passage provided, extract where the first session of Indian National Congress was held
The Indian National Congress conducted its first session in Bombay from 28 to 31 December 1885.