In God we trust - Wikipedia, the free encyclopedia

"In God we trust" was adopted as the official motto of the United States in 1956 as an alternative or replacement to the unofficial motto of E pluribus unum, adopted when the Great Seal of the United States was created and adopted in 1782.^[1][2]

In God we trust has appeared on U.S. coins since 1864^[3] and on paper currency since 1957.^[4]

Following the link on coins, I find the history behind it was an earlier degression:

History of 'In God We Trust'

The motto IN GOD WE TRUST was placed on United States coins largely because of the increased religious sentiment existing during the Civil War. Secretary of the Treasury Salmon P. Chase received many appeals from devout persons throughout the country, urging that the United States recognize the Deity on United States coins...

It was found that the 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. In December 1863, the Director of the Mint submitted designs for new one-cent coin, two-cent coin, and three-cent coin to Secretary Chase for approval. He proposed that upon the designs either OUR COUNTRY; OUR GOD or GOD, OUR TRUST should appear as a motto on the coins...

The Congress passed the Act of April 22, 1864. This legislation changed the composition of the one-cent coin and authorized the minting of the two-cent coin. The Mint Director was directed to develop the designs for these coins for final approval of the Secretary. IN GOD WE TRUST first appeared on the 1864 two-cent coin.

...The use of IN GOD WE TRUST has not been uninterrupted. The motto disappeared from the five-cent coin in 1883, and did not reappear until production of the Jefferson nickel began in 1938. Since 1938, 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. IN GOD WE TRUST was not mandatory on the one-cent coin and five-cent coin. It could be placed on them by the Secretary or the Mint Director with the Secretary's approval.

The motto has been in continuous use on the one-cent coin since 1909, and on the ten-cent coin since 1916. It also has appeared on all gold coins and silver dollar coins, half-dollar coins, and quarter-dollar coins struck since July 1, 1908.