The Census is designed to allocate seats in Congress, provide funding for citizens, and reflect the general living demographics of the United States. The Census should include a question about citizenship for a few reasons.
First off, this allows an accurate representation of United States citizens. Just because there is a question about citizenship does not mean it affects legal immigrants. The representation of the United States should be accurately judged on citizen status, not how many people live in one square block with an immigration center in the center.
Secondly, it allows the government to understand the flow of movement of people’s. The citizenship question is necessary for this and even if someone or a mass amount of immigrants put down “no,” it allows the government to see 1) where the bigger populations of immigrants live, 2) understands where the current stance of citizens live,, and 3) also understand the wider demographic and socio-economics of the population at large.
Citizenship is important to know for the census for Illinois and New York may lose seats by a large percentage to other states if immigrants are not counted towards the overall proportion of the state. I know many Democrats would be angry and appalled if the 3/5 rule for the Old South would apply for sanctuary cities and the states they are in, but that is only fair and reasonable to the other states who abide by Federal immigration policy.