An Act of Congress dated January 18, 1837, prescribed the mottoes and devices that should be placed upon the coins of the United States. This meant that the mint could make no changes without the enactment of additional legislation by the Congress.

Many people began turning back towards God during the Civil War, giving rise to a call to place the Motto "IN GOD WE TRUST" on United States coins. Secretary of the Treasury Salmon P. Chase received many appeals from devout persons throughout the country, urging that the United States to officially give recognition to God on United States coins.

During the tenure of Director Pollock the Rev. Mark Richards Watkinson (1824-1877), pastor of "The Old Ridley Baptist Meeting House" , sat down on November 13, 1861, and wrote then Treasury Secretary Salmon P. Chase. The letter read as follows:

Dear Sir:

You are about to submit your annual report to Congress respecting the affairs of the national finances.

One fact touching our currency has hitherto been seriously overlooked. I mean the recognition of the Almighty God in some form in our coins.

You are probably a Christian. What if our Republic were now shattered beyond recognition? Would not the antiquaries of succeeding centuries rightly reason from our past that we were a heathen nation? What I propose is that instead of the Goddess of Liberty we shall have next inside the 13 stars a ring inscribed with the words 'perpetual union'; within this ring the all-seeing eye crowned with a halo; beneath this eye the American flag, bearing in its field stars equal to the number of the States united; in the folds of the bars the words 'God, liberty, law.'

This would make a beautiful coin, to which no possible citizen could object. This would relieve us from the ignominy of heathenism. This would place us openly under the divine protection we have personally claimed. From my heart I have felt our national shame in disowning God as not the least of our present national disasters.

To you first I address a subject that must be agitated.

Within a week after receipt of Rev. Watkinson's letter, Secretary Chase sent a letter to the new Director of the Mint, James Pollock.

Dear Sir: No nation can be strong except in the strength of God, or safe except in His defense. The trust of our people in God should be declared on our national coins.

You will cause a device to be prepared without unnecessary delay with a motto expressing in the fewest and tersest words possible this national recognition.

In response to this directive Director Pollock came up with various wordings such as "Our Trust Is In God," "Our Trust in God," "Our God and Our Country," "God And Our Country," and "God Our Trust," . In December 1863, designs were submitted to the Secretary of the Treasury. On December 9, 1863, Secretary Chase wrote a reply to Director Pollock :

I approve of your mottoes, only suggesting that on that with the Washington obverse the motto should begin with the word, "Our," so as to read, "Our God And Our Country." And on that with the shield it should be changed so as to read, "In God We Trust."

Other organizations throughout the country were also pressing for similar National recognition of God’ presence in society.

On February 3, 1863, eleven Protestant denominations (including United Presbyterians and the Methodist Episcopalian General Conference) organized the National Reform Association. Their aim was to "reform" the Constitution and one of its principle purposes was to amend that document to "indicate that this is a Christian nation." The association formally petitioned Congress to amend the preamble of the Constitution so as to read:

We, the people of the United States, HUMBLY ACKNOWLEDGING ALMIGHTY GOD AS THE SOURCE OF ALL AUTHORITY AND POWER IN CIVIL GOVERNMENT, THE LORD JESUS CHRIST AS THE RULER AMONG THE

NATIONS, HIS REVEALED WILL AS THE SUPREME LAW OF THE LAND, IN ORDER TO CONSTITUTE  A CHRISTIAN GOVERNMENT, AND in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure THE INALIENABLE RIGHTS and the blessings of LIFE, liberty, AND THE PURSUIT OF HAPPINESS to ourselves, our posterity, AND ALL THE PEOPLE, do ordain and establish this Constitution for the United States of America.

This change was not enacted but did help in allowing the government to see the wisdom of placing our Nation in God’s hands and proclaiming our trust in Him on the medium of exchange; our coins.

 The National Reform Association attracted many eminent men into its ranks. These were men such as Supreme Court Justice William Strong, Prof. J. H. McIlvaine of Princeton, former governors J. W. Geary and James Pollock of Pennsylvania, J. M. Harvey of Kansas, and J. W. Stewart of Vermont. (President Lincoln picked James Pollock as the mint's tenth director in 1861, and he remained in that job until he resigned in 1867.)

Congress passed the Act of April 22, 1864 allowing "IN GOD WE TRUST" to appear on the 1864 two-cent coin. Another Act of Congress passed on March 3, 1865, it allowed the Mint to place the motto on all gold and silver coins..

On February 12, 1873 Congress passed the Coinage Act . It also said that the Secretary "may cause the motto IN GOD WE TRUST to be inscribed on such coins as shall admit of such motto." The use of IN GOD WE TRUST has not been uninterrupted. All United States coins bear the inscription. Later, the motto was found missing from the new design of the double-eagle gold coin and the eagle gold coin shortly after they appeared in 1907. In response to a general demand, Congress ordered it restored, and the Act of May 18, 1908, made it mandatory on all coins upon which it had previously appeared.

On July 30, 1956, the 84th Congress passed a law declaring "IN GOD WE TRUST" to be the national motto of the United States.(P.L. 84-140)Law 36 U.S.C. 186, titled "National Motto," and  states in its entirety:

“The national motto of the United States is declared to be 'In God We Trust",

Law 31 U.S.C. Section 324a, titled "Inscription on currency and coins," states in its entirety, At such time as new dies for the printing of currency are adopted, the dies shall bear, at such place or places thereon as the Secretary of the Treasury may determine to be appropriate, the inscription "In God We Trust" and thereafter this inscription shall appear on all United States currency and coins.

Matthew R. Rothert from Arkansas, was the president of the Arkansas Numismatic Society. Joining the American Numismatic Association in 1946, he was eventually elected president of that association for the 1965-1967 term. In a speech to the Arkansas group on November 11, 1953, he gave a speech concerning the idea of including "In God We Trust" on paper money. The response to his speech was well received and he quickly sent a written proposal to Secretary of the Treasury Humphrey, and also to President Eisenhower and Secretary of Commerce Sinclair Weeks.

On June 7, 1955, H.R. 619 "Providing for the inscription of 'In God We Trust' on all United States Currency and Coins," was introduced in the House. In the Congressional Record , June 7, 1955, page 7796, Congressman Bennet of Florida addressed his collegues as follows:

I sincerely hope that the Senate will give its prompt approval to this proposal. In these days when imperialistic and materialistic communism seeks to attack and destroy freedom, we should continuously look for ways to strengthen the foundations of our freedom. At the base of our freedom is our faith in God and the desire of Americans to live by His will and His guidance. As long as this country trusts in God, it will prevail. To serve as a constant reminder of this truth, it is highly desirable that our currency and coins should bear these inspiring words "In God We Trust."

On June 29, 1955, Lyndon Baines Johnson (D-TX) introduced Calendar No. 642, H.R. 619 "A bill to provide that all United States currency shall bear the inscription 'In God We Trust.' " The bill was quickly passed.

On March 22, 1956, H.R. Res. 396 was introduced to establish "In God We Trust" as a national motto. The bill became law on July 30, 1956 (36 U.S.C. Section 186).

Challenges

 American Atheists and others have mounted legal challenges to the constitutionality of the motto "In God We Trust" on the currency and coins in the past. Those attempts have been unsuccessful but even now cases are actively being fought by the American Center for Law and Justice.