| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 34,631 | 11,354 | 46,902 | |
| 2020 | D | 33,619 | 11,096 | 45,735 | |
| 2016 | D | 28,890 | 10,371 | 42,678 | |
| 2012 | D | 27,244 | 11,107 | 39,781 | |
| 2008 | D | 29,826 | 11,927 | 42,552 | |
| 2004 | D | 27,229 | 13,994 | 42,421 | |
| 2000 | D | 21,807 | 13,351 | 40,060 | |
| 1996 | D | 20,772 | 11,532 | 37,124 | |
| 1992 | D | 23,197 | 11,520 | 41,660 | |
| 1988 | D | 21,455 | 14,932 | 36,699 | |
| 1984 | D | 19,357 | 18,255 | 37,777 | |
| 1980 | R | 11,970 | 12,448 | 29,668 | |
| 1976 | R | 12,808 | 15,463 | 28,671 | |
| 1972 | R | 12,344 | 17,605 | 30,011 | |
| 1968 | R | 10,343 | 13,446 | 25,248 | |
| 1964 | D | 16,103 | 9,070 | 25,202 | |
| 1960 | R | 8,659 | 17,061 | 25,733 | |
| 1956 | R | 5,475 | 19,749 | 25,224 | |
| 1952 | R | 6,285 | 18,673 | 25,019 | |
| 1948 | R | 5,721 | 13,719 | 20,444 | |
| 1944 | R | 7,174 | 12,805 | 20,053 | |
| 1940 | R | 7,118 | 14,325 | 21,693 | |
| 1936 | R | 7,007 | 13,332 | 20,746 | |
| 1932 | R | 6,180 | 12,185 | 18,916 | |
| 1928 | R | 5,114 | 14,471 | 19,866 | |
| 1924 | R | 3,701 | 11,766 | 16,123 | |
| 1920 | R | 3,487 | 9,508 | 13,573 | |
| 1916 | R | 3,455 | 4,736 | 8,638 | |
| 1912 | D | 3,272 | 2,237 | 8,103 | |
| 1908 | R | 3,734 | 5,090 | 9,232 | |
| 1904 | R | 3,780 | 5,414 | 9,615 | |
| 1900 | R | 3,852 | 5,409 | 9,696 | |
| 1896 | R | 3,506 | 5,342 | 9,200 | |
| 1892 | R | 3,404 | 4,717 | 8,813 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Tompkins County's electorate is heavily shaped by Cornell University and Ithaca College, producing Democratic presidential margins that routinely exceed 50 points — among the widest of any county in the state.
The unraveling was not abrupt. The Democratic margin in Tompkins County peaked at fifty points in 2024; it narrowed steadily over the late twentieth century. The 1984 election delivered the county to the Republican party for the first time in many years, by a margin of three points. By 2024, the margin had widened further.
The economic and demographic context is severe. Tompkins County's median household income of $74,024 is among the lowest of any county in the United States; 16% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Denver County and Dane County.