It looks like the CDC page only reports the cases confirmed by CDC. I'm just guessing but it looks like the Johns Hopkins page reports those cases both confirmed by CDC and cases where state labs have identified positive results and waiting for CDC confirmation. For example: CDC = 938 cases; Johns Hopkins = 1,323.This is a great page to keep an eye on for numbers.
https://www.cdc.gov/coronavirus/2019-ncov/cases-in-us.html
https://www.arcgis.com/apps/opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6