In its early history Placer County was solidly Republican: it voted Republican in every election between 1860 and 1912, when Bull Moose nominee Theodore Roosevelt was California's official Republican nominee.[26] Between 1916 and 1976, however, the county voted Republican only in three landslide elections of 1920, 1952 and 1972 – in all of which its GOP margins were much smaller than for the state or nation. Since the “Reagan Revolution” Placer County has become and remained a stronghold of the Republican Party; it consistently elects Republican public officials and has voted for presidential candidates from the party in every election since 1980.

In the United States House of Representatives, Placer County is split between California's 1st and 4th congressional districts, represented by Doug LaMalfa (R–Richvale) and Tom McClintock (R–Elk Grove), respectively..