councillor vs councilmember

councillor

noun
  • A member of a council. 

  • In particular, a representative elected to a local authority, such as a city council: a city councillor 

councilmember

noun
  • A councilman or councilwoman; member of a council. 

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