This view of the least and most religious states is from the Gallup Poll. It comes from Gallup Polls done between January 1st and December 31st of 174.745 adults in all 50 states, and has a margin of error of only 1 point. They determined the religiosity of a state by looking at the percentage of people in that state who said religion was very important to them.
There was a pretty big difference among the states -- with Mississippi being the most religious (63%) and New Hampshire being the least religious (20%). I thought it was interesting that only 8 states had a majority of their citizens saying religion was very important to them. I think that speaks to the growing secularization of this country.
