Make sure that students know that population figures came from census. Explain that the number of Congressmen from each state is determined by the states population. Discuss how many congressmen their state has. Invite a representative from the congressman's local office to speak. If a computer is available students can create a data base using the information which they collected.
Students can make poster illustrating why they think participating in the census is important.
Ideas might include that it is valuable to know how many men and women there are who would be of an age for military service, how many very old people there are in an area who could use special support services etc. The posters can be the culminating activity.