The census man,
The day he came round,
Wanted my name
To put it down.
Hughes speaks of the decennial survey conducted by the United States government. This survey or  census  seeks to account for every person living on U.S. soil, so that taxes and congressional districts(and thereby number of seats each state gets within the house of representatives) can be appropriated to each state within the union. This can be found within  Article 1 Section 2  of the United States Constitution. 
 
 The census is also used to show the demographics of a given area, which can be used to determined whether the Representative within the house is  descriptively representative  of an ethnicity, religion, sex, etc. of a given congressional district.
Madam and the Census Man