What is known as the supreme law of the country

In the United States, the supreme law of the country is the Constitution.

Explanation:

The Constitution of the United States is the supreme law of the United States of America. It was adopted in its original form on September 17, 1787 by the Constitutional Convention of Philadelphia, Pennsylvania, and then ratified by the people at conventions in each state in the name of "We the People". It has a central place in American law and political culture. The United States Constitution is the oldest federal constitution currently in force in the world.

maybe ... Constitution