"Coleslaw" is an anglicization of the Dutch "koolsla" or cabbage salad. Its existence in the US would likely date back to the first Dutch colony in North America: New Netherland, which was first settled in the 1620s. As such, American coleslaw has a history of roughly 390 years and antedates American caselaw by a few decades.
You got me curious -- our first case with the modern term "coleslaw" is from 1935, in Rhode Island, and begins ominously with "The plaintiff in this case was injured by swallowing two small pieces of wire concealed in an order of beef stew, bread and coleslaw which she had purchased and was eating at defendant’s lunch counter."
Apologies that the link requires a login to view the full text, and for various other shortcomings in the current browsing experience. Also apologies to anyone who actually reads the coleslaw case -- caselaw is a scary place.