It was renamed the Apostolic Vicariate of Eastern Siam[1][2] on 10 September 1841, having lost territory to establish the Apostolic Vicariate of Western Siam.

On 5 May 1899 it lost more territory to establish the Apostolic Vicariate of Laos.

[1] On 9 February 1967 it lost territory to establish the Diocese of Nakhon Sawan as its suffragan.

It covers the administrative provinces Ayutthaya, Bangkok, Nakhon Pathom, Nonthaburi, Pathum Thani, Samut Prakan, Samut Sakhon and Suphanburi; also the parts west of the Bang Pa Kong River of Chachoengsao and Ban Na of Nakhon Nayok belong to the diocese.

Its ecclesiastical province comprises the Metropolitan's own archdiocese and these six suffragan bishoprics :