Geez Louise refers to a common minced oath, like Gosh or Jiminy Crickets, which were created in order to avoid saying the Lord’s name in vain, during the turn of the 20th century.
While the exact origin of “Geez Louise” is shrouded in the mist of the past, first traces of the expression emerge in the late 1920’s and early 1930’s.
This is supported by the fact that many other rhyming expressions, like “See you later, alligator” and “the bee’s knees” also started appearing in this time period.
An early newspaper example of the phrase can be dated back to 1957.
Over the 20th century, “Geez Louise” became increasingly popular across the United States, and later across the whole Anglosphere.
It was further popularized upon the release of Thelma and Louise in 1991, where Thelma even addresses Louise (portrayed by Geena Davis and Susan Sarandon respectively) as “Geez Louise”.
The expression was first defined on Urban Dictionary in 2004, with a couple of other entries having been uploaded since that time.