COVID-19 Infection Rates in SF Bay Area Counties

Updated November 21  2020 – As of November 18th the total number of positive tests for COVID-19 in the 6 Bay Area counties reached 112,070. The 6-County daily rate of change was 0.75% (It’s been between 3.29% and .21% since July 14 – the results of the past week doubled over the previous week – again!. We began a new spike in the last week of October!  This rate for the more than 6.6M population of the 6-county area is 1.68%; this is among the lowest for metropolitan infection rates in the country. We’re still in the rainstorm and cannot put away our umbrellas without severe consequences!




COVID-19 Data Sources


San Francisco  | San Mateo  | Marin  |   Santa Clara  | Alameda  | Contra Costa


Below is the number of days it’s taken to go from the first infection (approximately February 18, 2020) to rise to 10,000, 20,000, 30,000,  40,000, 50,000, 60,000, 70,000, 80,000, and 90,000 respectively.  

  1 to 10,000 87 days – May 15th
10,000 to 20,000 40 days – June 24th
20,000 to 30,000 15 days – July 9th
30,000 to 40,000 12 days – July 21st
40,000 to 50,000 11 days – August 1st
50,000 to 60,000 12 days – August 13th
60,000 to 70,000 13 days – August 26th
70,000 to 80,000 20 days – September 15th
80,000 to 90,000 27 days October 12th
90,000 to 100,000 23 days November 4th





The Bay Area doubling rate has improved since mid-August. The doubling rate was 40 days on August 15th. On November 3rd it increased to 236 days (it dropped from 238 last week). For the combined 6-county rate, this is the second longest (best) it’s been since March 16th, when we began recording infection rates.


Posted in COVID-19, Uncategorized.


  1. Would be good to use different colors for the counties instead of just different shades of brown. Hard to read. Thanks!

    • Thanks, Karen. These colors are a set of “safe colors” to deal with such issues as “blue-green color blindness” by us boys 😉

      You’re not the first to raise this. I will explore a different combination of colors for more contrast.

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