The Census was used to track jobs over time, from 1978 to 2014. The resulting map is intriguing. 

“Fewer and fewer farmers: Our map shows the tail end of a century-long trend. Farming technology (everything from tiny seeds to giant harvesters) keeps getting better, which means fewer and fewer people can grow more and more food.”

NPR. Map: The Most Common* Job In Every State. February 5, 2015. https://www.npr.org/sections/money/2015/02/05/382664837/map-the-most-common-job-in-every-state