Anyone or Any One

Grammarist clarifies the issue of anyone and any one as follows: Anyone is a pronoun that indicates any person. It is used when there are no qualifications to the grouping. Something could belong to anyone if there are no distinguishing marks or unique factors.

Unlike anytime and anymore, anyone is not simply an adverb form of any one and they are not interchangeable outside of the United States.

Any one is a term that means any single object or person. It is generally not listed in dictionaries except perhaps to distinguish the differences with anyone.