Where did let them eat cake come from?
No context provided
What country did the phrase "Let them eat cake" originate?
France
No context provided
Who is attributed to have originally said "Let them eat cake?
Marie Aintoinette
Let them eat cake
https://en.wikipedia.org/wiki/Let%20them%20eat%20cake
While the phrase is commonly attributed to Marie Antoinette, prior to the French Revolution, she did not originate it, and she probably never said it.
Let them eat cake
"Let them eat cake" is the traditional translation of the French phrase "Qu'ils mangent de la brioche",[1] said to have been spoken in the 17th or 18th century by "a great princess" upon being told that the peasants had no bread. 
Let them eat cake
"Let them eat cake" originated in France and is the traditional translation of the French phrase "Qu'ils mangent de la brioche".  This phrase is attributed to Marie Aintoinette, prior to the French Revolution, although she did not originate it, and she probably never said it. 