Gallup poll here on religious belief in the US. Total sample size is over 178000.
(page 1, with map and article here, but to me the numbers were the story.)
USA overall: 13.2%
States over 20%:
Maine, New Hampshire, Vermont, Oregon, Washington, Hawaii, Alaska
States under 10%:
North Dakota, Nebraska, North Carolina, Georgia, Tennessee, Alabama, Mississippi, Arkansas, Louisiana, Oaklahoma, Texas