The data folder contains daily COVID-19 case counts for each US county. The history starts on 2020-03-14.
- COVID tracking project: State-level positive & negative tests in the US
- CCSEGISandData: daily country & state-level case counts, also county-level data before 3/10
- New York Times COVID-19 dataset: US state & county-level historical data
- 1Point3Acres: US & Canada county-level cases & deaths
The data comes from this CSV file, which is maintained by CSBS.org. It's the data file behind their interactive county-level map.
CSBS originally announced their interactive map effort on twitter.