George Washington, Champion of Atheists... not so much...

You will often hear atheists attribute to George Washington the quote, "the Government of the United States of America is not, in any sense, founded on the Christian religion."

Two problems with that.  The first is the George Washington never said that.  The quote comes from the first Treaty of Tripoli, negotiated during Washington's administration and signed for the nation by John Adams.*  The second is that, like most such quotes it is both truncated and taken out of context.  The full quote:
"As the Government of the United States of America is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquility [sic], of Mussulmen [Muslims]; and, as the said States never have entered into any war, or act of hostility against any Mahometan nation, it is declared by the parties, that no pretext arising from religious opinions, shall ever produce an interruption of the harmony existing between the two countries." 

All it says, and rightly, is that, just as the Constitution stipulates, the United States has no formally adopted State religion. It also says the Muslims should stop attacking our ships but they apparently didn't read that part.

What did Washington think of Christianity?

The name of American, which belongs to you, in your national capacity, must always exalt the just pride of Patriotism, more than any appellation derived from local discriminations. With slight shades of difference, you have the same religion... reason and experience both forbid us to expect, that national morality can prevail in exclusion of religious principle...   George Washington, Farewell Address

It is impossible to account for the creation of the universe without the agency of a Supreme Being. It is impossible to govern the universe without the aid of a Supreme Being.  George Washington, A Life of Washington (New York: Harper & Brothers, 1835), Vol. II, p. 209.

What students would learn in American schools above all is the religion of Jesus Christ. George Washington, speech to the Delaware Indian Chiefs May 12, 1779

To the distinguished character of patriot, it should be our highest glory to add the more distinguished character of Christian.  George Washington, May 2, 1778, at Valley Forge

Almighty and eternal Lord God, the great Creator of heaven and earth, and the God and Father of our Lord Jesus Christ; look down from heaven in pity and compassion upon me Thy servant, who humbly prorate myself before Thee. George Washington's prayer at Valley Forge

The General hopes and trusts that every officer and man, will endeavor so to live, and act, as becomes a Christian Soldier defending the dearest Rights and Liberties of his country. General George Washington, July 9, 1776

The General most earnestly requires and expects...of all officers and soldiers, not engaged on actual duty, a punctual attendance on divine service, to implore the blessings of heaven upon the means used for our safety and defense.  General Orders. Fitzpatrick 3:309. (1775.)

The commander-in-chief orders the cessation of hostilities between the United States of America and the king of Great Britain to be publicly proclaimed tomorrow at twelve o'clock,...after which the chaplains with the several brigades will render thanks to almighty God for all his mercies, particularly for his overruling the wrath of man to his own glory, and causing the rage of war to cease among the nations....

The proclamation...must afford the most rational and sincere satisfaction to every benevolent mind, as it puts a period to a long and doubtful contest, stops the effusion of human blood, opens the prospect to a more splendid scene, and, like another morning star, promises the approach of a brighter day than has hitherto illuminated the Western Hemisphere; on such a happy day, a day which is the harbinger of peace, a day which completes the eighth year of the war, it would be ingratitude not to rejoice!  General Orders. Fitzpatrick 26:334. (1783.)

The honorable Continental Congress having been pleased to allow a chaplain to each regiment,...the colonels or commanding officers of each regiment are directed to procure chaplains accordingly, persons of good characters and exemplary lives, [and] to see that all inferior officers and soldiers pay them a suitable respect and attend carefully upon religious exercises. The blessing and protection of Heaven are at all times necessary, but especially so in times of public distress and danger.  General Orders. Fitzpatrick 5:244. (1776.)

The commander-in-chief directs that divine service be performed every Sunday at eleven o'clock in those brigades [in] which there are chaplains; those which have none [are] to attend the places of worship nearest to them. It is expected that officers of all ranks will by their attendance set an example to their men. While we are zealously performing the duties of good citizens and soldiers, we certainly ought not to be inattentive to the higher duties of religion. To the distinguished character of patriot, it should be our highest glory to add the more distinguished character of Christian. The signal instances of providential goodness which we have experienced, and which have now almost crowned our labors with complete success, demand from us in a peculiar manner the warmest returns of gratitude and piety to the Supreme Author of all good.  General Orders. Fitzpatrick 11:342. (1778.)

Divine service is to be performed tomorrow in the several brigades or divisions. The commander-in-chief earnestly recommends that the troops not on duty should universally attend with that seriousness of deportment and gratitude of heart which the recognition of such reiterated and astonishing interpositions of Providence demand of us.  General Orders. Fitzpatrick 23:247. (1781.)

During his inauguration, Washington took the oath as prescribed by the Constitution but added several religious components to that official ceremony. Before taking his oath of office, he summoned a Bible on which to take the oath, added the words "So help me God!" to the end of the oath, then George Washington leaned over and kissed the Bible.

Such being the impressions under which I have, in obedience to the public summons, repaired to the present station, it would be peculiarly improper to omit in this first official act, my fervent supplications to that Almighty Being, who rules over the universe, who presides in the council of nations, and whose providential aids can supply every human defect, that His benediction may consecrate to the liberties and happiness of the people of the United States.." "...Every step by which they have advanced to the character of an independent nation, seems to have been distinguished by some token of providential agency" From President George Washington's Inaugural Address, April 30th, 1789, addressed to both Houses of Congress.

Is it necessary that any one should [ask], "Did General Washington avow himself to be a believer in Christianity?" As well may we question his patriotism, his heroic devotion to his country. His mottos were, "Deeds, not Words"; and, "For God and my Country."  Nelly Custis-Lewis (Washington’s adopted daughter)

Let us with caution indulge the supposition, that morality can be maintained without religion.  George Washington, ca. 1789, Maxims of Washington, ed. John F. Schroeder (Mt. Vernon: Mt. Vernon Ladies Association, 1942), p. 106.

O Most Glorious God, in Jesus Christ, my merciful and loving Father; I acknowledge and confess my guilt in the weak and imperfect performance of the duties of this day. I have called on Thee for pardon and forgiveness of my sins, but so coldly and carelessly that my prayers are become my sin, and they stand in need of pardon.  George Washington

I have sinned against heaven and before Thee in thought, word, and deed. I have contemned Thy majesty and holy laws. I have likewise sinned by omitting what I ought to have done and committing what I ought not. I have rebelled against the light, despising Thy mercies and judgment, and broken my vows and promise. I have neglected the better things. My iniquities are multiplied and my sins are very great. I confess them, O Lord, with shame and sorrow, detestation and loathing and desire to be vile in my own eyes as I have rendered myself vile in Thine. I humbly beseech Thee to be merciful to me in the free pardon of my sins for the sake of Thy dear Son and only Savior Jesus Christ who came to call not the righteous, but sinners to repentance. Thou gavest Thy Son to die for me.  George Washington; from a 24 page authentic handwritten manuscript book dated April 21-23, 1752 William J. Johnson George Washington, the Christian (New York: The Abingdon Press, New York & Cincinnati, 1919), pp. 24-35.

No people can be bound to acknowledge and adore the invisible hand which conducts the affairs of men more than the people of the United States. Every step by which they have advanced to the character of an independent nation seems to have been distinguished by some token of providential agency...We ought to be no less persuaded that the propitious smiles of heaven cannot be expected on a nation that disregards the eternal rules of order and right, which heaven itself has ordained.   George Washington in his Inaugural Address, April 30, 1789

Although guided by our excellent Constitution in the discharge of official duties, and actuated, through the whole course of my public life, solely by a wish to promote the best interests of our country; yet, without the beneficial interposition of the Supreme Ruler of the Universe, we could not have reached the distinguished situation which we have attained with such unprecedented rapidity. To HIM, therefore, should we bow with gratitude and reverence, and endeavor to merit a continuance of HIS special favors. 1797 letter from George Washington to John Adams

Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports... And let us indulge with caution the supposition that morality can be maintained without religion... Reason and experience both forbid us to expect that national morality can prevail to the exclusion of religious principle. From President George Washington's Farewell Address

It is impossible to rightly govern the world without God and Bible.  George Washington  

*as for what John Adams thought: " "Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.”