Costin’s neighbors were mostly small tradesmen and government clerks, the majority of whom were white and some of whom enslaved people. Over the next 20 years, Costin amassed enough wealth to buy several more lots and houses. By the 1840s, he was one of the most prolific Black property owners in the nation’s capital.
Admitted to the upper echelons of D.C. society, Costin promoted causes related to the city’s growing Black community. In the 19th century, work opportunities and less restrictive racial codes (compared with neighboring Virginia) attracted an increasing number of free Black people to D.C. In 1800, nearly 30 percent of the city’s population was Black, but only around 20 percent of these individuals were free. By 1840, the city was still 30 percent Black, but 65 percent of these residents were free. The city had many race-based restrictions that made life more difficult for Black Washingtonians, including limits on the type of jobs they could have, so the community formed charitable organizations to help.
Costin served as the first president of the Resolute Beneficial Society, formed in 1818 to support the Black community on issues ranging from education to burials. He was also a founding member of D.C.’s first independent Black church, Israel Metropolitan Christian Methodist Episcopal Church (still in operation today), and belonged to the city’s first Black Freemasonry organization.
In addition to securing his own family’s freedom, Costin purchased and freed three enslaved people from his probable half-brother, Wash, in 1827. He raised one of them—a 4-year-old child named Montgomery Parke (possibly related to the Custises)—in his own family.
Opportunities to participate in antislavery efforts in D.C. were limited, as most activists were located further north, but Costin did take one bold step: a nonviolent protest of a new racist law in the city in 1821. The law required all free Black people to show written evidence of freedom, ask three white residents to vouch for their character and post a $20 bond that could be forfeited if they failed to conduct themselves properly or became impoverished. Those who refused could be fined, jailed or even expelled from the city—but Costin was apparently willing to take this risk. He had been living as a free man for nearly 20 years and would not bow to these new rules. The city fined him, but he didn’t back down, instead appealing to the D.C. Circuit Court.