Ganesh Chaturthi is a Hindu festival which is dedicated to celebrating the birthday of Lord Ganesha. Ganesha is the highly recognizable elephant headed god of the Hindus.
This festival is celebrated throughout the world: wherever there are devotees of Ganesha, you can expect for Ganesh Chaturthi to be celebrated, because it is one of the most (if not the most) important celebrations devoted to him no matter if you are in London or New York. Nevertheless, this festival is especially popular in India. This is not surprising, because it was here that the festival actually originated.
Certain parts of India are especially well known for celebrating this festival. It is especially popular in states such as Maharashtra, Gujurat and Telangana where you can expect to see huge public celebrations. In regions such as Goa and Tamil Nadu, the festival is still popular but it is more common for worshipers to celebrate it in the privacy of their own homes.