Iran has a total population of 81.16 million people. The worlds 18th most populated country. Most people live in the central plateau and speak Indo-Iranian Dialects. The capital city of Iran is Tehran with a population of 8 million. Christianity is reportedly the fastest growing religion in Iran. Another big city in Iran is Mashhad, and it is known as a place of religious pilgrimage. Full of golden domes and a circular complex tomb. This city has many cool museums full of old artifacts and very rare pieces of history.