Susan Jacoby wrote a great book on secularism in American history starting with the founding fathers called Freethinkers
Freethinkers: History of American Secularism
Great book. Starts with the role of secular elements in the formation of the US, and then goes on to talk about their role in emanicipation, woman's sufferage, and civil rights.
Not really a book. Someone else might. I could name a few that give interesting slices of the picture, but most will oversimplify and/or apply a particular a spin that missing much of the picture....
Two random books (with very different spins) that have almost nothing in common aside from being worth reading:
Freethinkers: A History of American Secularism
Founding Rivals: Madison vs. Monroe, The Bill of Rights, and The Election that Saved a Nation