Is John Locke the most important influence on the US Constitution?

NO, John Locke, Charles Montesquieu, and Jean-Jacques Rousseau all had an arguably equal influence. THOMAS PAINE WAS MORE INFLUENTIAL THAN ANY OF THEM. Read and learn - http://thomaspaine.org/aboutpaine/how-paine-transf...

The Magna Carta of 1215 greatly inspired the Founding Fathers.  The wording, phrases and ideas are all reflected in The Constitution and Bill of Rights.

Montesquieu, Locke, Blackstone, and the Bible are the four major influences.

His ideas certainly had an influence, but that was just one influence among many. James Madison, "the father of the Constitution" was college educated and well read in ancient and contemporary philosophy, as well as history and law. Likewise with many of his peers. Many of them also had practical experience as politicians and lawyers. Their personal experiences in the Revolution and with the weaknesses of the "Articles of Confederation" probably factored in more than anything else. 

No

(Of course not. THINK about that. Think about what you are asking.)