The county unit system was a voting system used by the U.S. state of Georgia to determine a victor in statewide primary elections, as well as some Congressional elections, from 1917 until 1962.

Though the county unit system had informally been used since 1898, it was formally enacted by the Neill Primary Act of 1917. The system was ostensibly designed to function similarly to the Electoral College, and so in practice the large ratio of unit votes for small, rural counties to unit votes for more populous urban areas provided outsized political influence to the smaller counties.

For the period this system was in effect, the Democratic Party was the single dominant party in state politics. Democratic nominees frequently ran unopposed or with only token opposition in general elections, so the Democratic primary election usually determined the eventual officeholder. This was combined with other devices, such as white primaries, to make sure that only the votes of white rural voters would be reflected in statewide elections.

Under the county unit system, the 159 counties in Georgia were divided by population into three categories. The largest eight counties were classified as "urban", the next-largest 30 counties were classified as "town", and the remaining 121 counties were classified as "rural". Urban counties were given 6 unit votes, town counties were given 4 unit votes, and rural counties were given 2 unit votes, for a total of 410 available unit votes. Each county's unit votes were awarded on a winner-take-all basis.

Candidates were required to obtain a majority of unit votes (not necessarily a majority of the popular vote), or 206 total unit votes, to win the election. If no candidate received a majority in the initial primary, a runoff election was held between the top two candidates to determine a winner.

The county unit system generated great controversy, since it gave the votes of counties with smaller populations a significantly greater weight than counties with larger populations. For at least the final two decades the system was in use, a majority of statewide unit votes were controlled by counties that, collectively, had less than one-third of the state's total population. Because of this, statewide candidates for office could (and frequently did) win the primary by winning the county unit vote while losing the overall popular vote, sometimes by large margins. This also gave rise to kingmakers such as Roy V. Harris, who were known for their ability to deliver the unit votes of many rural counties.

One of the most controversial elections of the county unit system era was the 1946 Democratic gubernatorial primary. By winning a large number of rural counties, Eugene Talmadge garnered a nearly 60% majority of the statewide county unit votes and won the primary, even though he lost the popular vote by 16,144 votes to James V. Carmichael, who himself only won a plurality, not a majority, of the popular vote.

Several lawsuits were filed in the 1940s and 1950s challenging the constitutionality of the system. These lawsuits were rejected by the U.S. Supreme Court on the grounds that apportionment issues should be handled by individual states. In 1962, however, the Supreme Court reversed its opinion, ruling in the Tennessee case of Baker v. Carr that redistricting issues present justiciable questions, thus enabling federal courts to intervene in and to decide reapportionment cases.