The COVID-19 epidemic data of US counties can be retrieved from the Wolfram Data Repository. Note that this dataset is updated daily, by curating the JHU data. In this very short essay, I show how to get county data and do some visualizations.
If you are retrieving the epidemic data on a daily basis, I suggest erasing the resource object, to avoid any potential issue with cached data.
Get COVID-19 epidemic data from the Wolfram Data Repository and select California counties:
For coloring and legends, I borrowed some ideas from this community post. In order to figure out how to set limits of bins, you can get some hints from the following code.
Generate a list of histogram bins and their heights from the number of confirmed cases, put them in the format of {bin range,height}, and return bins with nonzero height: