| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 43,438 | 58,678 | 102,918 | |
| 2020 | R | 46,029 | 56,068 | 104,123 | |
| 2016 | R | 35,559 | 51,961 | 92,402 | |
| 2012 | D | 43,986 | 43,240 | 89,013 | |
| 2008 | D | 47,303 | 46,348 | 95,272 | |
| 2004 | D | 47,602 | 47,111 | 96,580 | |
| 2000 | D | 47,781 | 40,952 | 93,270 | |
| 1996 | D | 44,203 | 31,438 | 89,444 | |
| 1992 | D | 35,649 | 30,401 | 96,584 | |
| 1988 | D | 43,801 | 42,537 | 86,868 | |
| 1984 | R | 41,368 | 51,289 | 92,858 | |
| 1980 | D | 40,405 | 38,760 | 86,394 | |
| 1976 | R | 43,667 | 46,101 | 90,239 | |
| 1972 | R | 38,991 | 54,777 | 94,091 | |
| 1968 | D | 41,999 | 38,796 | 87,925 | |
| 1964 | D | 67,260 | 28,663 | 95,985 | |
| 1960 | D | 51,680 | 50,001 | 101,765 | |
| 1956 | R | 30,161 | 62,433 | 92,594 | |
| 1952 | R | 36,504 | 54,843 | 91,499 | |
| 1948 | R | 34,119 | 35,858 | 72,219 | |
| 1944 | R | 34,850 | 37,614 | 72,666 | |
| 1940 | R | 33,207 | 36,729 | 70,101 | |
| 1936 | R | 29,207 | 30,144 | 61,415 | |
| 1932 | R | 20,765 | 30,852 | 52,891 | |
| 1928 | R | 16,881 | 33,229 | 52,453 | |
| 1924 | R | 7,993 | 25,874 | 38,062 | |
| 1920 | R | 7,416 | 21,193 | 31,032 | |
| 1916 | R | 8,367 | 12,212 | 21,224 | |
| 1912 | D | 7,647 | 5,654 | 18,808 | |
| 1908 | R | 8,574 | 11,145 | 20,356 | |
| 1904 | R | 7,550 | 10,881 | 19,155 | |
| 1900 | R | 7,726 | 9,352 | 17,601 | |
| 1896 | R | 6,441 | 8,626 | 15,490 | |
| 1892 | D | 6,850 | 6,663 | 14,537 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Niagara County, anchored by Lockport and the falls-adjacent city of Niagara Falls, shifted from a competitive swing county to a reliably Republican-leaning one as its industrial-era Democratic base eroded alongside manufacturing employment.
The county's recent history is a story of close margins. The Democratic margin reached forty points in 1964; the Republican margin reached forty-seven points in 1924. Most other elections have been decided by single-digit points.
Niagara County's demographics — a population of 210,721, a 83% non-Hispanic-white share, a median household income of $69,633 — situate the county close to national averages on several dimensions. The county's voting pattern over the last decade is most similar to that of Luzerne County and Alpena County.