If you are a foreign citizen and living in India for more than 180 days, you will have to register

If you are a foreign citizen and living in India for more than 180 days, you will have to register with the Indian Government.

The registration can be done in your city itself. If you are living in a major city, there are offices called FFRO. Say for example, if you are in Chennai - you can find an office like that in the city.

If you are living in a sub-urban (tier-II or tier-III) cities, you have an option of registering in Commissioner's office in your district. Say for example, in Madurai - you can do the same registration in Commissioner office.

You will have to get Originals and photocopies of the following and visit the Passport division of the Commissioner office in your district - Madurai.

1) Passport of the citizen.
2) Visa of the citizen
3) PIO of the citizen
4) Address proof for the citizen locally in India
5) Employment or Student identification locally in India.

Also don't forget to check the government India websites before you visit this office with the documents, for more documents are needed or not.

For children below 16 years, it is not required to register (even in india government websites it is mentioned), however in cases when we are returning to the country (example USA), the customs might ask for penalty over there which is unnecessary. So, to avoid this, it is better to register with the passport division of Commissioner office or FFRO office in your city/district.

Once you fill in the application and submit the photo copies of the documents (show your original also), then they submit it to the police department, which is verified in your house. The police station who checks will be the local police station near your home. Once that is done, a certificate is issued. If you are late in doing this after 180 days, then for the US citizen, it is charged $30.