The ratification process of the US Constitution occurred during what years?

The Constitution was ratified during the years 1787 to 1790. But it became effective on March 4, 1789 after its ratification by a ninth state, New Hampshire, on June 21, 1788.

The Constitution was completed on September 17, 1787, and at that point the process of ratification began. The first state to ratify it was Delaware, on December 7, 1787. According to the Constitution, it was to go into effect in those states that ratified it as soon as a total of nine states did so. The ninth state, New Hampshire, ratified it on June 21, 1788.

The last of the original thirteen colonies to ratify the constitution was Rhode Island, which did so on May 29, 1790.