Pew Religion Survey
That’s a lot of respondents and will be a treasure trove of information. Such a large sample size will allow analysts to study various religious subgroups with reasonable sample size.
Here is the first tidbit: Pew found that 1.7% of the respondents identified as Mormons. Extrapolating that number, rough and dirty, to a total population of 300 million Americans would mean that there are more than 5.1 million Mormons in the United States.
In reality, of course, one would have to be more careful since Pew only polled adults. Looking at the data about family size would allow us to arrive at a more precise estimate. 5.1 million Mormons is probably not too far off the precise figure.