Despite the fact that most of America speaks one language, there are distinctive sayings that are nearly incomprehensible to people from different parts of the country. In the South, there are phrases like "he's as drunk as Cooter Brown." In the Midwest, you have the multipurpose "You betcha!"
A fascinating map from Long Island University's Robert Delaney highlighted by Reid Wilson at The Washington Post shows that the divisions are even more complicated than you might think. He highlights 24 different distinctive dialects. If you add Alaska and Hawaii, which aren't pictured, there are even more.
These aren't just accents, but genuinely distinct ways of speaking beyond just the way words sound. 
"An accent refers only to the way words are pronounced," Delaney writes, "while a dialect has its own grammar, vocabulary, syntax, and common expressions, as well as pronunciation rules that make it unique from other dialects of the same language."
Here's the map:

And here are Delaney's descriptions of a few of the more obscure dialects you probably haven't heard of:
Hudson Valley (4)
New York was originally a Dutch colony, and that language influenced this dialect's development. Some original Hudson Valley words are stoop (small porch) and teeter-totter. They call doughnuts (which were invented by the Dutch) crullers and olycooks.
Pennsylvania German-English (12)
This was strongly influenced by Pennsylvania Dutch, a dialect of German spoken by people in this area (in this context, "Dutch" is actually a mispronunciation of the German word, "Deutsch," which means "German"). Its grammar allows sentences like "Smear your sister with jam on a slice of bread" and "Throw your father out the window his hat." They call doughnuts fasnacht, and they also invented dunking - from the German "dunken" (to dip).
Virginia Piedmont (20)
When an R comes after a vowel, it becomes UH, and AW becomes the slided sound, AH-AW. Thus, four dogs becomes fo-uh dahawgs. Some local words are: hoppergrass (grasshopper), old-field colt (illegitimate child), school breaks up (school lets out), weskit (vest).
Gullah (22)
Sometimes called Geechee, this creole language is spoken by some African Americans on the coastal areas and coastal islands of Georgia and South Carolina and was featured in the novel on which the musical, Porgy and Bess, was based. It combines English with several West African languages: Mende, Yoruba, Wolof, Kongo, Twi, Vai, Temne, Ibo, Ewe, Fula, Umbundu, Hausa, Bambara, Fante, and more. The name comes either from the Gola tribe in Liberia or the Ngola tribe in Angola. The grammar and pronunciation are too complicated to go into here, but some words are: bad mouth (curse), guba(peanut - from which we get the English word goober), gumbo (okra), juju (magic), juke (disorderly, wicked), peruse (to walk leisurely), samba (to dance), yam (sweet potato).
Read the full list of descriptions here