The US Census Bureau just released the 2010 official population counts. DC had a count of 601,723 which is an increase of 5.2% from 2000. This is the first decade of population growth in 6 decades.
Data from the Master Address Repository (MAR) was instrumental in raising DC's population count. Using the MAR the MAR Data Team was able to add over 17,000 addresses (primary & secondary) to the Census' Master Address File (MAF). This definitely contributed to a higher population count. More information can be found in the LUCA Report.