Captain William Chrysostom Dermody was a dedicated and outspoken abolitionist who was killed in the Civil War. He was born in Nova Scotia, Canada, in 1830 but came to New York with his family as a young child. He volunteered with the 67th New York Infantry and served in Company K, the first regiment of Long Island volunteers. The backbone of the regiment was formed by members of Henry Ward Beecher’s Abolitionist Plymouth Church Congregation in Brooklyn Heights. It was organized in Brooklyn on June 24, 1861, and the soldiers left for Washington, D.C., on August 21, 1861. The regiment fought in many battles throughout the war, including the Battle of Spotsylvania.

The Battle of Spotsylvania took place in Fredricksburg, Virginia, from May 8 to 21 in 1864. A numerically superior Union force met with a smaller but vigorous Confederate force anxious to avenge their previous losses at Gettysburg. During the two weeks of the battle, a total of 152,000 men fought (100,000 Union soldiers and 52,000 Confederate) and 30,000 lives were lost. During May 12 and 13 in particular, Gen. Ulysses Grant managed to capture nearly an entire division of Gen. Robert E. Lee’s army and came close to cutting the Confederate army in half. It was at this point that Dermody lost his life, being mortally wounded on May 12 and dying the following day. His remains were buried on the battlefield at the time. In 1865, the Fredericksburg National Cemetery was established to reinter and memorialize the almost 20,000 soldiers who died there. A marker for Dermody can be found in the cemetery. His parents, Patrick and Lavinia Boyd Dermody, are buried in Flushing's Mount St. Mary Cemetery.

The plot of land located on 216th Street and 48th Avenue had been the site of the local two-room schoolhouse. In 1866, the site was dedicated to the memory of Captain Dermody by a ceremonial meeting of a Union and Confederate veteran, each planting a special tree: a maple to represent the North and a sycamore to represent the South. The trees were to grow together as a symbol of the communal hope for a better union. A monument was placed in the square with the inscription, “For a Better Union 1861-1865”; it remains there today. Every Memorial Day, the Bayside Historical Society lays a wreath at the park to commemorate Captain Dermody and those who fought in the Civil War.

The Board of Aldermen (predecessor of the City Council) officially named this property for Captain William C. Dermody on March 15, 1937. The name was changed simply to Captain Dermody Triangle on July 29, 1997, by an executive decree from Commissioner Henry J. Stern. A low stone wall bounds the triangle.