Pew Research reports:
There were about 3.3 million Muslims of all ages living in the United States in 2015. This means that Muslims made up about 1% of the total US population (about 322 million people in 2015), and we estimate that that share will double by 2050.
Certain states, such as New Jersey, have two or three times as many Muslim adults per capita as the national average.
Our projections suggest the US Muslim population will grow faster than the Hindu population and much faster than the Jewish population in the coming decades. Indeed, even before 2040, Muslims are projected to become the second-largest religious group in the U.S., after Christians. By 2050, the American Muslim population is projected to reach 8.1 million people, or 2.1% of the total population.
Just over half of the projected growth of the American Muslim population from 2010 to 2015 is due to immigration. Over the last 20 years, there has been an increase in the number of Muslim immigrants coming to the US The number of Muslim immigrants currently represents about 10% of all legal immigrants arriving in the US, and a significantly smaller percentage of unauthorized immigrants.
The other main cause of Islam’s recent growth is natural increase. American Muslims tend to have more children than Americans of other religious faiths. Muslims also tend to be younger than the general public, so a larger share of Muslims will soon be at the point in their lives when people begin having children.
There has been little net change in the size of the American Muslim population in recent years due to conversion. About one-in-five American Muslim adults were raised in a different faith or none at all. At the same time, a similar number of people who were raised Muslim no longer identify with the faith. About as many Americans become Muslim as leave Islam.