During his senior year, a group of 34 students, that did not include Chaplin, initiated a rebellion that caused them to be dismissed.

Theodosia Gilbert, born on April 11, 1855, married Reverend Frederick John Clegg Walton.

[12] In 1846, he moved to Washington, DC, and filled the position left by Charles Turner Torrey when he died in prison that year;[13] Chaplin became an agent for the Underground Railroad.

[10] The Vigilance Committee provided funding for purchasing enslaved blacks and for the rescue of fugitive slaves.

[10] For instance, in November 1848 he negotiate the payment to free the Mary and Elizabeth Edmonson, who were fugitives during the Pearl incident.

In December 1848, Chaplin made a call for direct action: "to storm the castle of tyranny and rescue from its cruel grasp its bruised and peeled victims".

[10] In August 1850, Chaplin was arrested for aiding in the escape of two slaves, Allen and Garland H. White,[10][13][18][a] who were owned by then-congressmen Alexander Hamilton Stephens[b] and Robert Toombs of Georgia, respectively.

A $500 reward was set for both slaves and John H. Goddard, the pro-slavery captain of the night guard and police magistrate, was hired to search for them.

[6][10] Based upon a tip, Goddard and his posse waited for the escapees, who had been picked up by a carriage and taken to the Maryland-Pennsylvania border.

[23][24] The events were recorded in a pamphlet entitled The Case of William L. Chaplin; being an Appeal to all Respecters of Law and Justice against the cruel and oppressive treatment to which, under color of legal proceedings, he has been subjected, in the District of Columbia and the State of Maryland.

"[6] A historical marker at the Howard County Courthouse in Ellicott City, Maryland, states that it was the location for judicial proceedings related to legal cases involving those charged with encouraging enslaved persons to run away... Arguably, the most famous case involved the transfer of known Underground Railroad agent William L. Chaplin of New York from Montgomery County to Howard County in 1850 but there were many cases involving local free Blacks like that of Warner Cook, charged with enticing those enslaved to run away.

It was organized by Charles Bennett Ray and Gerrit Smith of the New York State Vigilance Association and attended by Frederick Douglass and Mary and Elizabeth Edmonson, who were fugitives during the Pearl incident and subsequently ran away.

[2] James C. Jackson, Joseph C. Hathaway, and Chaplin split from other abolitionists and joined the Free Democratic party.