over there vs therein

over there

adv
  • In that place; there (at some distance). 

  • overseas to Europe (for military engagement), especially to the Western Front in France during World War I 

  • To that place; thither (at some distance). 

therein

adv
  • in that; in that place; in him/her/it. 

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