Yoga is most popular in India. This is no surprise, because India is the birthplace of yoga and yoga is very closely allied to ancient Indian religions such as Hinduism, Buddhism and Jainism.
In addition, the ancient Indian scriptures of the Bhagavad Gita are seen to be the earliest texts that relate to yoga.
However, statistics show that the practice of yoga is popular in other countries in the world. Around 9.5% of the adult population of the US has practiced yoga, for example. Yoga is also very popular in Namibia. Again, this is not surprising: in the eighteenth century, Indian gurus began traveling westwards. As they went exploring, reaching as far as Europe and (later) beyond, they taught the local populations about Indian religion and culture. One of the key things that they brought to the West was yoga. So, we can see that the popularity of yoga in the West is something that has been developing for a few centuries already.