Do universities keep your college application materials, if you are rejected? I guess I am just being curious, but I was wondering whether college applications are kept or saved (i.e common app) by the institutions you applied to? 
I assume that if you are accepted they are pretty much kept until you graduate. But what happens to the application materials of people who have not being accepted? All those applications are kept for some period of time and then disposed? 
Thanks!
This would depend on many things, including the laws of the country in which the University is situated. I assume that in some places it is mandatory and others forbidden. In those places without such laws it probably is determined locally by the University itself. 

I believe that in the US, many, if not most, college applications now are done electronically through an agency or organization with the applicant determining who can obtain the materials. For example, see https://www.commonapp.org. In such a case, the organization likely retains the materials, subject to the law, of course. 

If you have a specific worry, about a specific University, you could ask them and get the correct answer, of course.