Hint: It starts with an "I".
Let me clarify that I'm referring to the years 2007 to 2014, when two Pew studies were taken.
I came across this while doing research on the relative predominance of Muslim prayers, events, commemorations and so on in current American culture. For example, each of the 2016 Democratic and Republican political conventions had one Muslim invocation or prayer (out of a rough total of ten). But what about, say, Buddhists or Hindus? More on that in another post.
Here are the actual numbers, expressed in % of the population:
I'm not surprised that the Christian numbers went down. Nor am I surprised that the Muslim numbers went up. But I was very much surprised that the Muslim numbers more than doubled in just seven years.
I was surprised that Mormonism went down. I had always assumed that the exponential growth of that group was unstoppable. I was also surprised that Judaism went up.
As you can see, the "Asian" religions - Islam, Buddhism and Hinduism - are now roughly tied in numbers, though Islam has moved ahead, almost certainly to stay. Hinduism went sharply up, though not as much as Islam, while Buddhism held the line.
The population of the United States was roughly 300 million in 2007 and 320 million in 2014, so you can multiply the % numbers by 3 (or a bit more than 3) to get the absolute numbers of adherents, expressed in millions.
While the proportion of Muslims is still much lower than that of most Western European countries, the absolute numbers are in many cases similar. The United States now has about as many Muslims as the United Kingdom, for example.
Unlike much of Western Europe, for Muslims, we're still not in the 4%-10% range, which often translates into 20% to 40% in some cities. I believe that only Flint, Michigan and a few other smaller Michigan towns are at that point.
But, obviously the momentum is with Islam. The proportion of Muslims in the United States more than doubled in seven years. I would assume the absolute numbers (given the increase in total population) came close to tripling in the last ten years.