St Andrew’s (Portuguese church), the oldest church in Chennai predating St. Mary's!!

1700: plan of Fort St. George, Madras (Chennai (TN). britishempire.co.uk

 There  has been a general consensus among historians and heritage lovers that the very first church built under the the early colonial rulers of  Madras is  St Mary’s church  located inside  Fort St. George  on the beach road, Chennai.  According to an article published in The Hindu (dated 19 Feb. 2018) by Sri Muthaih who, in the past, wrote quite interesting articles on the various aspects of Vintage Madras city, St Andrew’s,  a Roman Catholic  church dating back to 1642, is the oldest one predating  historical St. Mary's by 50 long years.  It was built by  Fr. Ephraim de Nevers with permission from Andrew Cogan, the  Agent of Fort St George, a British settlement in Madras. As  numerous Portuguese employees and the local fishermen community out side the fort  needed spiritual and divine services, Fr.Ephraim   convinced  the Capuchin Friar  who was to leave for Burma, to stay in Madras to take care of Church activities.
Services were held in the shed-like church in the initial stages and a school was functioning under the church. Fr. Ephraim taught English, Portuguese, etc  to Europeans and the Indian children also attended the school.  An interesting fact is Fr. Ephraim allowed the British to worship in the church whenever it was free.  St. Mary's School on Armenian Street  is an off-shoot of this old school. Owing to break in continuity in its history, the school  loses its claim to be the oldest Western-style school in British India. A permanent structure housing the church came up in  1675. It was rebuilt again in 1721, perhaps to rival, in the north, St Mary’s in the south

The first church in British Madras .thehindu.com

St. Andrew’s, the Portuguese Church,  was just outside the north wall of the Inner Fort was known as  Portuguese Square.  Both St. Mary's and Portuguese churches fell within the confines of Fort  St. George  when the outer walls were built in 1666 as part of additional fortification.
Ttt-bits:

St. Mary's church, Madras (Chennai), Alamy

St. Mary's church, Madras (Chennai). bl.uk/on

Above image: A vintage photo of St. Mary’s Church in Fort St George, Madras, Tamil Nadu, taken by Frederick Fiebig in c.1851. It is the oldest surviving Anglican church in the East. It was built  50 years later  after the Portuguese Church had been built  in Madras, by Sir Streynsham Master, Governor of Madras between 1678-81, Designed by William Dixon, the Master Gunner of the Fort, consecration took place in 1680. The tower of St. Mary's was completed in 1701, a steeple added in 1710, It is inside Ft. St. George that was constructed in the early 1640 by the British East India Company as its headquarters of the Coromandel Coast and marked the  earliest foundation of Madras city.This church, inside the fort, is steeped in history. It was here in the old prayer house solemnized the marriages of both Robert Clive,  the man who laid the foundation for the British Empire by capturing Bengal  and Elihu Yale who  served as a governor of Fort St. George, and a vestryman and treasurer of St Marys Church. His later gift of money to Cotton Mather helped in the foundation of Yale University in the USA which recently ran into  problems regarding its connection with the slavery  in the southern USA.

https://en.wikipedia.org/wiki/St._Mary%27s_Church,_Chennai
https://www.thehindu.com/society/history-and-culture/the-first-church-in-british-madras/article22795898.ece