On Monday, April 26, 2021, the U.S. Census Bureau announced that the number of people living in the United States as of April 1st, 2020 totaled 331,449,281.
The 2020 Census Bureau State population totals determine how many seats each state can hold in the House of Representatives.
You can read more here: https://www.cnn.com/2021/04/26/politics/us-census-2020-results/index.html
As expected, Illinois is among the seven states that will lose one seat in the U.S. House of Representatives, according to the Census Bureau announcement of the redistribution of the 435 congressional seats based on population shifts in the 2020 Census.
You can read more here: https://www.census.gov/newsroom/press-releases/2021/2020-census-apportionment-results.html
Read related Chicago Sun-Times article here: https://chicago.suntimes.com/2021/4/26/22403917/illinois-congress-seats-house-representatives-reapportionment-census-population
You can find the change in resident population of the 50 states, the District of Columbia and Puerto Rico (1910-2020) as released by the U.S. Census Bureau here.