Census workers have begun to go out into the streets to get an accurate number of homeless, itinerant and otherwise "uncountable" citizens. Meanwhile, we go to India, where the world's biggest census starts today as the country aims to get an accurate picture of their 1.2 billion citizens.
Mike Geissinger, is the local census office manager for Reno, Nevada. He shares the the difficult challenges of counting Reno's "uncountable" citizens - those without homes.
But spare a thought today for the 2.5 million census workers in India, who will be starting the massive task of counting India’s population. The whole process will take month and will include taking photographs and fingerprints of every citizen over the age of 15 to build the world’s biggest identity database. The BBC’s Delhi correspondent Sanjoy Majumder joins us from Delhi to tell us more.