Here’s an interesting map:

That comes from the Daily Yonder (link currently unavailable) courtesy of the Rural Blog, which says:

The 125 most rural districts analyzed by the Yonder had at least 33 percent of their population living in rural areas. The rural average of all 435 House districts is 21 percent. “There are 39 rural districts that switched from Democratic representation to Republican,” Bishop and Ardery write. “These account for 65 percent of the 60 seats Republicans captured from Democrats on Tuesday.” No Republican district on the most rural list switched to Democrat.