Mary Ann's story about the census is interesting from another standpoint.
If counting illegals gave 4 extra House seats to Texas, perhaps a new census that left them out would lead to reapportionment of those seats back to northern states like New York and Illinois. More electoral votes back in the hands of blue state politicians. Not to mention less Federal resources flowing to states like Texas. Kind of a silver lining sort of deal.
I don't know if the change would have that kind of effect especially for Illinois. There's been a mass migration of citizens out of Illinois since Rauner got in.
The purpose of the census is to determine how many people are living in the U.S. and where. If there are families or households who don't complete the census and have U.S. citizens within that household, there will be inaccurate numbers.
From the U.S. Census Bureau:
"The U.S. Census is mandated by the Federal government. In Article 1 Section 2 of the United States Constitution, it mandates that an official count be taken of the population."
"First off, it is important to know that the House of Representatives are numbered based on the number of constituents in their state. The same goes for the Electoral College. Since these two very important groups of people are based on the number of constituents in each state, a count must be taken every ten years to determine how many people there actually are in each state, and in the United States in total."
"Secondly, the U.S. Census is important for the purposes of distributing funds to the public. Taking a count of the people in the country helps the Federal government decide what areas of the population are in need of what services such as: welfare, housing projects, parks and other things mandated by the federal government."http://www.censusquestions.com/us-census.html
Without an accurate total, many U.S. citizens would not be adequately served by the federal government but that's the idea behind changing the census.