irreligion vs nontheism

irreligion

noun
  • The state of being irreligious; irreligious sentiment or thought. 

nontheism

noun
  • Any of a range of concepts regarding spirituality and religion which do not include the idea of a deity in the form of a theistic god or gods. 

How often have the words irreligion and nontheism occurred in a corpus of books? (source: Google Ngram Viewer )