| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 12,863 | 30,240 | 43,635 | |
| 2020 | R | 12,677 | 28,952 | 42,283 | |
| 2016 | R | 9,788 | 25,427 | 36,907 | |
| 2012 | R | 13,072 | 19,518 | 33,356 | |
| 2008 | R | 14,329 | 19,018 | 33,939 | |
| 2004 | R | 14,602 | 22,262 | 37,134 | |
| 2000 | R | 13,670 | 18,142 | 33,254 | |
| 1996 | R | 13,418 | 13,551 | 32,400 | |
| 1992 | R | 12,814 | 15,057 | 35,792 | |
| 1988 | R | 14,255 | 20,207 | 34,800 | |
| 1984 | R | 13,748 | 22,109 | 36,165 | |
| 1980 | R | 13,750 | 20,608 | 36,290 | |
| 1976 | R | 18,939 | 19,283 | 38,876 | |
| 1972 | R | 13,885 | 25,912 | 40,385 | |
| 1968 | R | 17,013 | 22,366 | 41,899 | |
| 1964 | D | 28,082 | 17,046 | 45,244 | |
| 1960 | R | 22,233 | 27,568 | 49,841 | |
| 1956 | R | 17,141 | 28,583 | 45,765 | |
| 1952 | R | 17,789 | 28,861 | 46,769 | |
| 1948 | R | 16,478 | 23,535 | 40,485 | |
| 1944 | R | 20,333 | 21,995 | 42,450 | |
| 1940 | D | 26,315 | 22,914 | 49,368 | |
| 1936 | D | 31,849 | 21,758 | 54,318 | |
| 1932 | D | 23,114 | 17,982 | 42,564 | |
| 1928 | R | 19,249 | 30,949 | 50,490 | |
| 1924 | R | 7,571 | 17,516 | 31,177 | |
| 1920 | R | 9,854 | 17,288 | 29,581 | |
| 1916 | D | 9,333 | 8,722 | 19,384 | |
| 1912 | D | 6,802 | 2,371 | 19,144 | |
| 1908 | R | 8,590 | 10,439 | 20,087 | |
| 1904 | R | 5,936 | 11,219 | 17,977 | |
| 1900 | R | 7,989 | 8,366 | 16,951 | |
| 1896 | R | 7,367 | 8,659 | 16,756 | |
| 1892 | D | 6,942 | 6,170 | 13,727 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Northumberland's Susquehanna River towns reflect the broader realignment of deindustrialized Appalachian Pennsylvania: a county that voted within single digits as recently as 2008 shifted to R+39.9 by 2024.
The Democratic margin in Northumberland County peaked at twenty-four points in 1964. By 1968 the county had flipped, voting Republican for the first time in many years. The 2024 margin was forty points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Northumberland County's median household income of $60,583 sits well below state and national norms, and 13% of residents live below the federal poverty line. The shift here is part of a broader realignment of working-class places across the country. The county's voting pattern over the last decade is most similar to that of Pulaski County and Washington County.