List of 2020 Primary Dates By State

The FEC has published their preliminary list of 2020 presidential and congressional primary elections dates. The first Congressional primary is as soon as March 3 in Alabama, Arkansas, California, North Carolina and Texas and the last Congressional primary takes place September 15 in Delaware and Massachusetts. Note that the presidential and congressional primary dates differ in some states and that all the dates are tentative and subject to change. See the FEC's list of dates below.

Source: https://www.fec.gov/resources/cms-content/documents/2020pdates.pdf