Dialect Survey Maps (the maps take a long time to load) which highlight the differences in regional dialects in the continental United States. This morning, through Open Culture, I learned about the Dictionary of American Regional English (DARE) which also demonstrates the differences in dialects in the United States.
DARE is a dictionary of words and phrases that are unique to different regions and states within the U.S. Visitors can browse for words according to region and state or simply enter a word into the search box. DARE is a subscription service, but it does offer 100 words for free to all visitors.
Applications for Education
I might use DARE in a geography course or U.S. History course to have students learn a bit about the culture of different parts of the country. I would have students pick a word or two from the list and research it to try to determine how and why it became used in a region. For example, by looking at DARE we know that the word "lutefisk" is mostly commonly used in the upper midwest. I would ask students to think about why the word is used there, but not in the south or west.
(Hint for any of my students that might come across this, the answer is connected to immigration patterns).