In December 1841, when Mother M. Delphine Hart and her intrepid band of 11 Loreto nuns arrived in Calcutta from Ireland, they were housed in "a splendid three-storeyed mansion, Number 5, Middleton Row, a noble building, spacious, airy..." Earlier occupants of the building included Henry Vansittart, Governor of Bengal (1760-64) Sir Elijah Impey, First Chief Justice of the Supreme Court at Calcutta (1774-82) and from 1824, the Second Anglican Bishop of Calcutta, Bishop Heber. On January 10, 1842, Loreto House school was opened in this building.

Meanwhile, the construction of St. Thomas' Church, on the same premises had begun from November 11, 1841. The Catholic Archbishop of Calcutta, Mgr. Carew, also constructed a residence for himself next to the church and at the doorstep of Loreto House. This building was then known as St. Thomas' House.

By the turn of the century, as Loreto House school grew larger, there was pressing need for more space. In 1897, a severe earthquake caused St. Thomas' steeple to topple. As part of their construction plans, the old Loreto House building was extended. A few years later, St. Thomas' House was purchased from the Archbishop, to be used at first for Infant School classes. On February 2nd 1912, the newly established Loreto College was housed there.

As the old Loreto House building was still not large enough, in 1926, No. 8 Middleton Row was purchased. Gradually, on the combined grounds of No. 7 & No. 8 St. Anne's building came up, all this included housing for the nuns as well as a kitchen and a large concert hall (1939); the new buildings of Loreto House school, parallel to Middleton Street and adjacent to St. Thomas' Church (1941) and then a three storey wing at right angles to Middleton Street (1950s).

Meanwhile, the city architects had declared the old Loreto House building to be unsafe. From 1958 to 1961, it was demolished and the new Loreto House was constructed. As the requirements of the college had also grown apace, classes shifted entirely to this new edifice. The only original buildings on the premises now are St. Thomas' Church and a part of the building where the college was first established. The Provincial of the Loreto institute in India now resides within the walls that first housed Loreto College. The College has been awarded ‘Heritage' status certified by the KMDA.