Information that is considered common knowledge does not need to be cited, but it can be difficult to decide what common knowledge is! It is important to keep in mind the following:
Common knowledge refers to information that it known by nearly everyone and is information that is listed in numerous places and can be found easily. Often, it can be found in general reference materials.
Examples of common knowledge information could be:
Denver is the capital of Colorado
Peaceful assembly is covered under the 1st Amendment
The Star-Spangled Banner is the national anthem
But, if you’re ever in doubt if something is considered common knowledge or if a citation is needed, include the citation!