COVID-19 Infection Rates in SF Bay Area Counties

Updated September 13  2020 – As of September 9th the total number of positive tests for COVID-19 in the 6 Bay Area counties reached 77,493. The 6-County daily rate of change was 0.62% (It’s been between 3.29% and .31% since July 14 – there was a bit of a spike in mid-August, but it has flattened some since then.  Hopefully, the trend in reducing the number of positive cases over the past few weeks will continue – if we continue good practices.  See the line chart (third chart). 

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 and 70,000 respectively.  

  1 to 10,000 87 days
10,000 to 20,000 40 days
20,000 to 30,000 15 days
30,000 to 40,000 12 days
40,000 to 50,000 11 days
50,000 to 60,000 12 days
60,000 to 70,000 13 days


The Bay Area doubling rate has improved since mid-August. The doubling rate was 40 days on August 15th. On September 9th it increased to 149 days. Let’s hope this trend continues!


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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