Eire vs Erin

Eire

name
  • The island of Ireland, consisting of the Republic of Ireland and Northern Ireland 

Erin

name
  • Ireland. 

  • A town in Wisconsin. 

  • A town in New York. 

  • An unincorporated community in Texas. 

  • A town in Ontario. 

  • A city, the county seat of Houston County, Tennessee. 

  • A female or male given name, in use since the mid-20th century, used in honor of Ireland. 

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