The most densely populated region in India is the Northern Region.

Explanation:

The Northern Region of India comprises several states, including Uttar Pradesh, Bihar, Punjab, Haryana, Rajasthan, and Delhi, among others. This region is known for its high population density compared to other regions of the country. Here is a detailed explanation of why the Northern Region is the most densely populated:

1. Uttar Pradesh:
Uttar Pradesh, the most populous state in India, is located in the Northern Region. It alone accounts for a significant portion of India's population. With an area of approximately 243,290 square kilometers, it is home to over 200 million people. The population density of Uttar Pradesh is high due to factors such as high birth rates, lack of proper family planning, and limited access to education and healthcare facilities in certain areas.

2. Bihar:
Bihar, another state in the Northern Region, has the second-highest population density in India. It is densely populated due to factors such as high fertility rates, limited employment opportunities, and inadequate infrastructure.

3. Punjab and Haryana:
Punjab and Haryana, known as the agricultural heartland of India, also contribute to the high population density in the Northern Region. These states have a high population density due to fertile land, irrigation facilities, and opportunities for employment in the agricultural sector.

4. Delhi:
Delhi, the capital of India, is located in the Northern Region. It is a major metropolitan city and experiences continuous migration from various parts of the country. Delhi's population density is attributed to factors such as better employment opportunities, educational institutions, and healthcare facilities.

5. Migration:
The Northern Region attracts a significant number of migrants from other parts of India in search of better livelihood opportunities. The migration to this region further contributes to its high population density.

Conclusion:
Considering the factors mentioned above, including the high population of Uttar Pradesh, Bihar, Punjab, Haryana, and continuous migration to the Northern Region, it can be concluded that the Northern Region of India is the most densely populated region in the country.