I know this is very late, but I don't think we ever did this for 2016. Somewhere, there is states' strongest swing/trend by county, for all preceding elections, but I can't find it.
Dem Rep
Alabama Shelby Lawrence
Alaska
Arizona Yuma Greenlee
Arkansas Benton Randolph
California Orange Lake
Colorado Broomfield Crowley
Connecticut Fairfield Windham
Delaware New Castle Kent
Florida Orange Glades
Georgia Forsyth Chattooga
Hawaii Honolulu Kauai
Idaho Madison Shoshone
Illinois DuPage Henderson
Indiana Hamilton Scott
Iowa Johnson Howard
Kansas Johnson Cherokee
Kentucky Fayette Elliott
Louisiana East Baton Rouge Assumption
Maine Cumberland Oxford
Maryland Howard Caroline
Massachusetts Norfolk Berkshire
Michigan Washtenaw Ogemaw
Minnesota Hennepin Swift
Mississippi Hinds Tishomingo
Missouri Boone Clark
Montana Gallatin Deer Lodge
Nebraska Douglas Box Butte
Nevada Elko Pershing
New Hampshire Rockingham Coos
New Jersey Somerset Cumberland
New Mexico Los Alamos Guadalupe
New York Westchester Franklin
North Carolina Wake Robeson
North Dakota Billings Kidder
Ohio Delaware Monroe
Oklahoma Oklahoma Nowata
Oregon Washington Wheeler
Pennsylvani Chester Schuylkill
Rhode Island Bristol Kent
South Carolina Charleston Chester
South Dakota Lincoln Jerauld
Tennessee Williamson Grundy
Texas Collin Duval
Utah Utah Carbon
Vermont Chittenden Essex
Virginia Arlington Alleghany
Washington King Grays Harbor
West Virginia Monongalia Calhoun
Wisconsin Ozaukee Forest
Wyoming Teton Platte
As expected, almost all of the strongest Dem swinging counties are: university counties, largest city or county, suburb of largest metro in/near state, Mormon, ski resort, where Trump consistently underperformed.
The others are:
Elko, NV
Billings, ND
Bristol, RI
Billings was Romney's best county in ND and all swung Repub, so it makes this list because it had the least room to swing. Any explanation of the other two?
The strongest swinging Repub counties by state are mainly non-distinctive rural areas, though the list contains two Hispanic counties (Duval, TX and Guadalupe, NM), a plurality Native American county (Robeson, NC), and a county with many white rural liberals (Berkshire, MA).