Most national and regional retailers rely on data from market research firms to make site location decisions. That market research data is typically heavily driven by the Census and aged/prorated in the intermediate years by factoring in growth in USPS delivery statistics. This method allows market research firms to keep pace with growth in population but cannot accurately capture the change in composition of a small area geography. Therefore growth will often be represented as more of the same.
Image from Census.gov's American Fact Finder
The geography unit in the map above is called a Census Block Group. The Mount Vernon Triangle falls entirely within Block Group 3 of Census Tract 47. The Block Group boundary goes east to 1st Street NW in some sections effectively including the Gales School and Golden Rule Apartments with the Triangle.
American Fact Finder will share Summary File 1 & 3 data although some data from these sources, like economic characteristics, are only returned for areas larger than a Block Group.
Click to enlarge; Stats from Census.gov's American Fact Finder
The top section of the statistics is Total Population which is divided into Population in Households and Group Quarters. Several different types of institutions qualify as group quarters including nursing homes, military, prisons, college, etc. In this case I'm assuming the Group Quarters population is from homeless shelters. The remainder of the statistics I included in the display are represented as Household counts rather than Population counts.
Many more interesting statistics are available on the American Fact Finder including that 67% of households were occupied by only person and the median monthly rent was $268. I would say the area continues to be comprised heavily of single person households but the rents sure have changed.
UPDATED: (12/14 2:35PM) - I found more Census 2000 statistics for this block group on FreeDemographics.com.
Click to enlarge; Stats from FreeDemographics.com