His brother Silas Casey III was a rear admiral in the United States Navy and commander of the Pacific Fleet from 1901 to 1903.

[4] His eldest son, Thomas Lincoln Casey Jr., graduated from West Point in 1879, served in the Corps of Engineers, and retired from the Army as a colonel in 1912.

[6] After a leave of absence ending February 25, 1867, Casey served as superintending engineer on the construction of Forts Preble and Scammel from March 1 to November 18, 1867.

Casey, then a lieutenant colonel and head of the Office of Public Buildings and Grounds in Washington, D.C., was known for his engineering skills and financial trustworthiness.

He developed an ingenious method to balance the foundation as workmen with picks shovels dug from either side in a coordinated effort.

[2] Over 130 years later, after the monument was damaged by an earthquake in 2011, engineers tasked with repairing the structure consulted Casey's original papers to understand how it was built.

"[2] He also was on several boards: to study the effect of a dry dock companies work on Portland Harbour in April 1868, to make torpedo cable contracts and examine systems of torpedo defence from May 26 to October 13, 1873, to advise on the ventilation of the United States House of Representatives March 1877 to March 1881, and February 15, 1884, to September 1886, and to advise on public works in the District of Columbia from 1879 to 1888.

[8] He then oversaw the construction of the Army Medical Museum and Library beginning April 14, 1885 and the erection of the James A. Garfield Monument from July 2, 1885.

[9] He oversaw construction on the Thomas Jefferson Building, which houses the Library of Congress, beginning on October 2, 1888;[8] it was nearly completed when he died suddenly on March 25, 1896.

[11] Casey was elected a member of the National Academy of Sciences in 1890,[4] and made an officer of the Legion of Honor of France[12] for his work on the Washington Monument.

[4] Casey was a member of the Society of the Cincinnati,[13] succeeding his father in 1882, and a Companion of the Military Order of the Loyal Legion of the United States until his death.