Counties with longest historical runs of voting for one party for President

[mianfei]

All dates below are inclusive:

Alabama

• D: Covington, Crenshaw, Henry, Houston, Lamar, Mobile, Pickens, Pike, Tallapoosa, Tuscaloosa (to 1944). All voted I in 1948, and Covington, Crenshaw, Henry, Lamar, Pickens, Pike, Tallapoosa and Tuscaloosa never voted R up to and including 1960
• R: Baldwin, Houston, Lee, Mobile, Shelby (1972 onwards) All voted I in 1968. Houston has not voted D from 1960 onwards.

Arizona

• D: Greenlee (1912-1996)
• R: Maricopa, Yavapai (1952-)

Arkansas

• D: Calhoun, Dallas, Izard, Saline, White (1852-1964). All voted I in 1968, R in 1972 when no county voted D
• R: Benton, Sebastian (1952-)

California

• D: Mariposa (1852-1916)
• R: Orange (1940-2012), Sutter (1944-); note also Alameda (1860-1928)

Colorado

• D: Costilla (1928-)
• R: Elbert (1936-)

Connecticut

• D: Hartford (1988-)
• R: Litchfield (1888-1960)

Delaware

• D: Kent (1856-1892)
• R: New Castle (1916-1932), Sussex (2000-)

Florida

• D: Bradford, Hamilton (1852-1964). Both voted I in 1968, R in 1972 when no county voted D
• R: Indian River, Lake, Lee, Manatee, Martin, Sarasota (1948-)

Georgia

• D: Hancock (1852-1968)
• R: Fannin (1920-1972)

Hawaii

• D: Hawaii, Honolulu, Kauai, Maui (1988-)
• R: Honolulu (1980-1984)

Idaho

• D: Clearwater, Lewis (1932-1968)
• R: Clark (1936-)

Illinois

• D: Union (1828-1948)
• R: Carroll (1856-2004)
• Carroll County, Illinois never voted D from creation in 1839 until Obama carried it in 2008.

Indiana

• D: Brown (1840-1948)
• R: Porter (1856-1992)

Iowa

• D: Dubuque (1960-2012), Johnson (1964-)
• R: Cass, Page (1936-)
• Marshall County, Iowa, never voted D from creation in 1846 up to and including 1960, but voted I in 1912.

Kansas

• D: Wyandotte (1976-)
• R: Doniphan (1864-)

Kentucky

• D: Floyd (1852-2004)
  
• R: Clay, Owsley (1864-)
• Jackson County, Kentucky has never voted D (in fact no Democrat has reached even 30 percent of the county’s vote) since being founded in 1858.

Louisiana

• D: Livingston (1840-1960)
• R: Bossier, Jefferson, Lafayette, La Salle, Ouachita, St. Tammany, Union (1972-). All voted I in 1968 and Bossier has the longest streak of not voting D, having never voted D from 1948 onwards.

Maine

• D: Cumberland, Hancock, Knox, Sagadohoc, York (1992-)
• R: Androscoggin, Cumberland, Franklin, Kennebec, Oxford, Penobscot, Piscataquis, Somerset, Waldo, York (1856-1908).
• Somerset did not vote D between 1840 and 1960 inclusive
• Franklin, Oxford, Penobscot and Piscataquis not between 1856 and 1960 inclusive

Maryland

• D: Queen Anne’s (1864-1948)
• R: Garrett (1916-). Founded in 1872 and has never voted D, voting I in 1912

Massachusetts

• D: Suffolk (1928-)
• R: Franklin (1856-1960)

Michigan

• D: Wayne (1932-)
• R: Missaukee, Ottawa, Sanilac (1916-)
• All three voted I in 1912
• Missaukee was organized in 1871 and has never voted D
• Ottawa last voted D in 1864
• Sanilac last voted D in 1852

Minnesota

• D: Ramsey (1928-)
• R: Carver, Otter Tail (1936-)

[mianfei]

Again, all dates are inclusive:

Mississippi

• D: Alcorn, Benton, Calhoun, Choctaw, Covington, Greene, Harrison, Itawamba, Issaquena, Jones, Leake, Lee, Neshoba, Newton, Perry, Pontonoc, Prentiss, Scott, Simpson, Smith, Tippah, Tishomingo, Union, Winston (1872-1944)
• R: Choctaw, Clarke, Forrest, Harrison, Jackson, Jones, Lamar, Lauderdale, Lincoln, Lowndes, Newton, Rankin, Scott, Simpson, Smith (1972-). All voted I in 1968, though Clarke was a tie in 1980. Forrest has not voted D from 1948 onwards.

Missouri

• D: Monroe (1864-1980)
• R: Gasconade (1860-)

Montana

• D: Deer Lodge (1928-)
• R: Beaverhead, Fallon, Powder River, Stillwater, Sweet Grass (1940-)

Nebraska

• D: Butler, Howard, Saline (1924-1948)
• R: Keya Paha (1920-)

Nevada

• D: Mineral (1928-1952); Clark (1992-)
• R: Douglas (1940-)

New Hampshire

• D: Coös (1864-1892)
• R: Cheshire (1856-1960)

New Jersey

• D: Warren (1840-1916)
• R: Ocean (1856-1908; did not vote D from 1850 founding up to 1960 inclusive)

New Mexico

• D: Rio Arriba, San Miguel (1960-)
• R: Lincoln (1940-)

New York

• D: Bronx, Kings, New York (1928-)
• R: Allegany, Broome, Cayuga, Chautauqua, Chenango, Cortland, Delaware, Essex, Fulton, Genesee, Jefferson, Livingston, Madison, Onondaga, Ontario, Orleans, Oswego, St. Lawrence, Saratoga, Schuyer, Tioga, Warren, Washington, Wayne, Wyoming, Yates (1856-1960)

North Carolina

• D: Northampton (1900-)
• R: Yadkin (1868-; never voted D since formation in 1850)
• Wilkes County, North Carolina has never voted D from 1836 onwards

North Dakota

• D: Rolette (1956-)
• R: Golden Valley, Grant, Kidder, Logan, McIntosh, Mercer, Sheridan (1940-)

Ohio

• D: Brown, Holmes (1832-1924)
• R: Clinton, Meigs, Warren (1856-1960)

Oklahoma

• D: Bryan, Choctaw, Coal, Johnston, Love, McCurtain (1908-1968)
• R: Major (1936-)

Oregon

• D: Columbia (1932-2012)
• R: Josephine (1940-)
• Also note Tillamook County, Oregon voted R every election 1860-1928

Pennsylvania

• D: Greene (1832-1924)
• R: Delaware, Lancaster (1860-1960); Snyder, Union, Wayne (1916-)
• Union has never voted D from 1836 onwards
• Snyder has never voted D from 1860 onwards
• Wayne has never voted D from 1896 onwards

Rhode Island

• D: Providence (1976-)
• R: Washington (1856-1960)

South Carolina

• D: Spartanburg, Union (1868-1944)
• R: Aiken (1956-)
• Lexington has never voted D from 1948 onwards, but voted I in 1948 and 1956

South Dakota

• D: Shannon/Ogala Lakota (1956-)
• R: Lawrence (1920-)

Tennessee

• D: Franklin, Humphreys, Marshall, Stewart, Tipton (1844-1964). All voted I in 1968. Stewart never voted R up to and including 2004.
• R: Cocke (1868-)
• Cocke, Sevier and Johnson have never voted D from 1836 onwards.

Texas

• D: Starr (1896-)
• R: Kendall (1936-)

Utah

• D: Carbon (1928-1952)
• R: Kane (1920-)

Vermont

• D: Addison, Chittenden, Franklin, Grand Isle, Windham (1988-)
• R: Addison, Bennington, Rutland, Washington, Windham (1856-1960). Of these, only Washington had ever voted D even before 1856, previously doing so in 1848

Virginia

• D: Franklin (1852-1964); voted I in 1968, R in 1972
• R: Floyd (1916-)
• Floyd County, Virginia, last voted D in 1880

Washington

• D: Grays Harbor (1932-2012)
• R: Adams (1940-)

West Virginia

• D: Webster (1868-1968)
• R: Morgan (1864-; last voted D in 1848)

Wisconsin

• D: Douglas (1932-)
• R: Walworth (1916-)

Wyoming

• D: Sweetwater (1928-1968)
• R: Crook, Johnson (1936-)

[Skill and Chance]

So Starr County, TX is the only Solid South county streak to survive into the Obama/Trump era.  Fascinating.