The Department of Social Services is a division of the Department of Integration. It has made its debut in the show since the pilot episode. This is where the protagonist of the series, Mark Lilly, works. The department has organized a class for new immigrants to New York City where many of the show's recurring characters attend.
The Social Services Department's job is to help new immigrants adapt to the society of New York. The city may be strange and foreign to some of them, as in the case of Quaggle, a troll who wasn't aware of the concept of money before the DOI has stepped in and helped him.
However, in the pilot episode, the Social Services Department's resources get slashed and most of its employees are laid off, leaving only two of them, Mark Lilly and Leonard Powers, to work there. Thus, all immigrants have been slapped together into a class which Mark runs.
And since Mark often has his hands full and Leonard has grave alcoholic and motivational problems, the DOI rather often fails at helping the immigrants and much more cases of immigrants needed to be integrated in New York are made evaporated than actually solved.
The Department of Social Services has been temporarily shut down by Twayne Boneraper in "Kong of Queens" because Mark and Leonard has not laughed at Twayne's joke in the meeting. It is reinstated when Callie Maggotbone points out it is essential in increasing the creature-to-human ratio, leading to a diminishing human population and the "End of Days" for mankind.