| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 6,610 | 8,379 | 15,105 | |
| 2020 | R | 6,914 | 8,329 | 15,608 | |
| 2016 | R | 5,697 | 7,236 | 13,980 | |
| 2012 | D | 7,094 | 5,889 | 13,266 | |
| 2008 | D | 7,422 | 7,038 | 14,741 | |
| 2004 | R | 6,979 | 7,981 | 15,325 | |
| 2000 | D | 6,841 | 6,734 | 14,338 | |
| 1996 | D | 6,825 | 5,004 | 13,955 | |
| 1992 | D | 5,810 | 5,432 | 14,974 | |
| 1988 | R | 6,215 | 7,221 | 13,571 | |
| 1984 | R | 4,825 | 9,420 | 14,307 | |
| 1980 | R | 5,010 | 7,174 | 13,690 | |
| 1976 | R | 5,745 | 7,659 | 13,508 | |
| 1972 | R | 4,441 | 9,368 | 13,842 | |
| 1968 | R | 5,222 | 7,083 | 13,005 | |
| 1964 | D | 8,890 | 4,473 | 13,376 | |
| 1960 | R | 5,693 | 8,741 | 14,435 | |
| 1956 | R | 3,623 | 10,417 | 14,040 | |
| 1952 | R | 4,328 | 9,669 | 14,020 | |
| 1948 | R | 4,897 | 7,266 | 12,516 | |
| 1944 | R | 4,236 | 7,424 | 11,688 | |
| 1940 | R | 4,203 | 8,364 | 12,598 | |
| 1936 | R | 4,295 | 7,919 | 12,454 | |
| 1932 | R | 4,764 | 6,502 | 11,486 | |
| 1928 | R | 3,873 | 7,911 | 11,938 | |
| 1924 | R | 7,103 | 22,583 | 31,584 | |
| 1920 | R | 3,023 | 6,260 | 9,696 | |
| 1916 | R | 2,845 | 3,307 | 6,505 | |
| 1912 | D | 2,573 | 2,336 | 6,211 | |
| 1908 | R | 3,136 | 3,749 | 7,101 | |
| 1904 | R | 3,288 | 3,823 | 7,278 | |
| 1900 | R | 3,461 | 3,787 | 7,399 | |
| 1896 | R | 3,213 | 3,853 | 7,198 | |
| 1892 | D | 3,199 | 3,112 | 6,707 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Seneca County sits between Cayuga and Seneca lakes, with a small population split between agricultural townships and the village of Waterloo. It backed the Republican presidential nominee by nearly 12 points in 2024, continuing a rightward shift from its closer margins a decade ago.
The Democratic margin in Seneca County has rarely exceeded thirty-three points in modern history; the Republican margin has rarely exceeded forty-nine points. 2024 delivered the county to the Republican candidate by twelve points.
Seneca County's demographics resemble the country more than they resemble most counties. A 88% non-Hispanic-white share, a 14% poverty rate, and a median household income of $68,089 — all within the broad national range. The county's voting pattern over the last decade is most similar to that of Cayuga County and Sullivan County.