| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 37 | 448 | 487 | |
| 2020 | R | 53 | 460 | 516 | |
| 2016 | R | 40 | 454 | 499 | |
| 2012 | R | 67 | 431 | 503 | |
| 2008 | R | 132 | 400 | 537 | |
| 2004 | R | 95 | 467 | 564 | |
| 2000 | R | 77 | 358 | 439 | |
| 1996 | R | 117 | 274 | 430 | |
| 1992 | R | 78 | 274 | 443 | |
| 1988 | R | 94 | 302 | 398 | |
| 1984 | R | 61 | 337 | 398 | |
| 1980 | R | 122 | 271 | 398 | |
| 1976 | R | 194 | 217 | 411 | |
| 1972 | R | 88 | 304 | 396 | |
| 1968 | R | 160 | 169 | 428 | |
| 1964 | D | 267 | 175 | 443 | |
| 1960 | R | 240 | 241 | 481 | |
| 1956 | R | 185 | 226 | 413 | |
| 1952 | R | 156 | 290 | 447 | |
| 1948 | D | 222 | 61 | 302 | |
| 1944 | D | 223 | 106 | 375 | |
| 1940 | D | 336 | 77 | 413 | |
| 1936 | D | 265 | 37 | 302 | |
| 1932 | D | 258 | 12 | 270 | |
| 1928 | R | 94 | 96 | 192 | |
| 1924 | R | 109 | 111 | 223 | |
| 1920 | D | 72 | 33 | 106 | |
| 1916 | D | 115 | 29 | 144 | |
| 1912 | D | 50 | 9 | 62 | |
| 1908 | — | — | — | — | |
| 1904 | — | — | — | — | |
| 1900 | — | — | — | — | |
| 1896 | — | — | — | — | |
| 1892 | — | — | — | — | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
McMullen County's 851 residents make it among the smallest electorates in Texas, yet it consistently records some of the widest presidential margins in the state, reflecting the deep Republican alignment of its ranching-dominated South Texas interior.
The unraveling was not abrupt. The Democratic margin in McMullen County peaked at ninety-one points in 1932; it narrowed steadily over the late twentieth century. The 1968 election delivered the county to the Republican party for the first time in many years, by a margin of two points. By 2024, the margin had widened further.
The economic and demographic context is severe. McMullen County's median household income of $43,875 is among the lowest of any county in the United States; 12% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Grant County and Antelope County.
