Undercount is one of the issues that plagues Census counts, and though officials are hoping to see reductions, many challenges face enumerators.
"The lingering effects of the recession make it harder to find and count people. Millions of U.S. residents are now jobless or homeless - with no fixed address. One out of eight housing units is vacant nationwide; the rate in Washington state is about one in 20.
Furthermore, an influx of immigrants - legal and illegal - over the past two decades make the counting that much tougher.
The Census Bureau realized in recent years that it missed significant numbers of new immigrants in the 2000 count - including many from countries where mistrust of government is common."