The purpose of this manuscript is to present a reliable estimate of the Muslim population and its percentage in each country throughout the world. This data is summarized to be a reference for other studies and discussions related to Muslim population. The presented data show that Asia has 69% of the world Muslim population while Africa has 27%. In addition, Muslims constitute 24% of the world population, or 1.65 billion people. This is expected to increase by over one percentage point each decade, reaching one out of four by 2020 and one out of three by 2075.