The 2015 Homeless Point in Time survey was just released locally from the Metropolitan Washington Council of Governments. This is the best effort each year to capture and count the number of adults, children, and families who do not have secure, ongoing housing.
For those who are interested in the issue of homelessness in our community, this is always a must-read document: http://www.mwcog.org/uploads/pub-documents/oV5bWls20150513103051.pdf
The data from the report comes from a Point In Time Survey, a method that involves hundreds of volunteers heading out to find as many individuals and families who are homeless or staying in temporary shelter to conduct a short survey. This survey always happens on a cold night, when many more people might choose to head to a shelter.
You can read some of the local coverage and reporting from these links:
Washington Post - http://www.washingtonpost.com/local/dc-politics/the-dc-region-has-11623-homeless-people-but-thats-not-the-whole-story/2015/05/13/41997f50-f984-11e4-9ef4-1bb7ce3b3fb7_story.html