Every 10 years, all U.S. states redraw their legislative and congressional districts in order to comply with the constitutional mandate that districts be equally populated. States redraw these districts using block-level data from the decennial census conducted in years ending in zero.

For the upcoming redistricting cycle, states were expected to receive census data by the end of March 2021, and, under normal circumstances, most would complete the process of redrawing maps by the end of summer 2021. However, in light of the ongoing Covid-19 emergency, the U.S. Department of Commerce and the U.S. Census Bureau announced on April 13 that there would be significant alterations and delays to census field operations. In conjunction with those delays, the Bureau said that it would ask Congress for a four-month extension of the statutory deadline for delivering redistricting-related data to the states. This would push the delivery of data from February–March 2021, as currently scheduled, to as late as the end of July 2021.

https://www.brennancenter.org/our-work/research-reports/how-changes-2020-census-timeline-will-impact-redistricting