A visa is needed for travel to India, including the state of Tamil Nadu. The Government of India requires that all foreign nationals seeking an entry into India, submit an Indian Visa Application.
This process of application filing can be done either by a physical visit to the Indian embassy or by completing the India Visa Application online (https://indianvisaonline.gov.in/). In the online Visa Application, when the Immigration Officer has approved, the electronic eVisa for India is dispatched to your email id.
The E-Visa needs to be applied for online in advance of travel and travellers must possess a machine readable passport.