hereupon vs immediately

hereupon

adv
  • Immediately afterwards; at this. 

immediately

adv
  • In an immediate manner; instantly or without delay. 

conj
  • directly (as soon as), instantly, the moment that. Indicates that the independent clause describes something that occurs immediately after the dependent clause's referent does. 

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