Note: Hello, person reading this. Just so you know, it's not uncommon for the origins of popular sayings to be unknown, and so if that happens, what I'll do is list the plausible theories that talk about a phrase's origin. If no theories are included, well, then I'll usually list the oldest known quote of an expression being used in writing to give you an idea on at least how old it is. Most of the time, these quotes will come from books, newspapers, or poems.

Alright, that's all. - An Alphabetical List of Common Expressions
The origin of this phrase is believed to be from Aesop, a Greek fabulist who is said to have lived around the time of 620 to 560 BCE. He wrote a number of different fables known collectively as Aesop's Fables.

One of the stories credited to his name tells of a young boy who was given the responsibility of watching over some sheep for the night. The boy eventually grew bored with his assignment and thought it would be rather humorous if he pretended to be in danger, so he started shouting "wolf, wolf!" His plan worked, as the people nearby heard his cries for help and came rushing to lend their support, only to learn that it was all a silly ruse. 

After this repeated a few more times, the people wisened up and no longer responded to the boy's deceitful cries. Later on, a real wolf showed up, and now the boy seriously started to cry for help, but it was too late, because nobody would listen to him any longer.

Indeed, when someone constantly lies, they lose the trust of others. Thus, the phrase 'crying wolf' is thought to have originated from this story; it references the lying boy.
* This is the third time my wife has complained about seeing a mouse running around the kitchen. I began to think she was crying wolf, but then I saw the small rodent for myself.

* My friend told me multiple times that his vacuum cleaner was not working, but it seems he was crying wolf because it works fine for me.

C - a list of sayings.
Phrases and Idioms
Lying; someone who calls for help when they don't actually need it.

Typically used to describe a person who frequently lies or complains about 
things when there are no real problems present.
The meaning of the phrase 'boy who cried wolf.'
Origins of the saying 'boy who cried wolf.'
C-Letter Sayings  |  Common Idioms and Phrases  - Their Definitions and Origins