CRS Insight – Apportionment and Redistricting Following the 2020 Census, April 27, 2021: “…The Clerk of the House sends each governor a certificate indicating a state’s number of Representatives within 15 calendar days of receiving the President’s apportionment message. Each state receives the number of Representatives noted in the President’s statement, beginning at the start of the next session of Congress (typically, early January of a year ending in “3”). States may then engage in their own redistricting processes before the start of that Congress, and the timing of redistricting varies based on state laws…”

See also 2020 Census Apportionment Results Delivered to the President April 26, 2021 – Release Number CB21-CN.30 – “The U.S. Census Bureau announced today that the 2020 Census shows the resident population of the United States on April 1, 2020, was 331,449,281. The U.S. resident population represents the total number of people living in the 50 states and the District of Columbia. The resident population increased by 22,703,743 or 7.4% from 308,745,538 in 2010…”