"In God We Trust" is not America's national motto. "E pluribus unum" is.
The phrase was added to currency in 1955 -- long after the country was founded.
Both these statements are false. "In God We Trust" is our national motto, since 1956. Before that, we had no official national motto. The Wikipedia page on it has a good reference.
Its history on currency is more complex (again, see the Wikipedia article), but it was first used on currency in 1861, and first appeared on paper currency in 1957.