While the San Diego County Board of Supervisors is officially a nonpartisan institution, Republicans controlled four out of the five supervisory seats, while a Democrat held one.

However, the election resulted in a Democratic majority for the first time in decades after Nora Vargas and Terra Lawson-Remer respectively won supervisorial elections in the first and third districts.

Even though county supervisor elections are officially nonpartisan in California, Republicans held a 4–1 majority in the San Diego County Board of Supervisors heading into the 2020 election, with the one being a lone Democrat.

[1] In the general election, Democrats Nora Vargas and Terra Lawson-Remer respectively won supervisory seats in the first and third districts, assuring a Democratic majority in the next term and for the first time in a generation.

[2] On January 5, 2021, the Board of Supervisors elected Nathan Fletcher as the new chair, succeeding Greg Cox.