At the age of forty-four, on September 18, 1861, Adam Cratsenberg enlisted in the first year of the Civil War as a private at Watertown, N.Y., in the 35th New York Infantry. By the following month, he was promoted to first sergeant of Company I. Although old enough to be the father of most of his comrades, Cratsenberg's patriotism had compelled him to take up arms for his country. He was honorably discharged on June 5, 1863, from the infantry; however, on November 10, 1863, he re-enlisted in the 14th New York Heavy Artillery, again rising to first sergeant of his unit, Company M.

According to reports, Cratsenberg fought in the battles of Rappahannock Station, Antietam, Fredericksburg, the Wilderness, Spottsylvania Court House, and Cold Harbor. At the latter battle, on June 2, 1864, he lost an arm and was taken prisoner by the Confederates, being paroled from Libby Prison in Virginia on August 13, 1864 . He was later discharged at Annapolis, Maryland, on January 20, 1865, on account of his wounds. Five days later he successfully applied for an invalid's wartime pension, which he received until his death.

Although a tanner and currier before the war, shortly after his discharge, Cratsenberg accepted an appointment as keeper of the Tibbetts Point Lighthouse, a position he held for about twenty years. A staunch Republican, Cratsenberg feared he would lose his position after the election of Grover Cleveland, the first Democratic president following the Civil War, and decided to resign before he could be replaced by a Democratic appointee. At about that time, he injured his hip, which would afflict him for the remainder of his life.

1850 U.S. Census for Denmark, Lewis Co., NY:
Adam Cratsenburgh M 33 New York; tanner & ?
Esther A Cratsenburgh F 31 New York
Charlotte Maria Cratsenburgh F 11 New York
Phebe Cratsenburgh F 9 New York
John C Cratsenburgh M 7 New York
Idah Cratsenburgh F 5 New York
Ellen Cratsenburgh F 3 New York

In the 1855 NY State Census, the Cratsenbergs were living in Utica, Oneida Co., NY but Charlotte wasn't with them.

1870 U.S. Census for Cape Vincent, Jefferson Co., NY:
A J Cratsenburg M 53y New York
E A Cratsenburg F 52y New York
C H Cratsenburg M 14y New York
May B Cratsenburg F 10y New York
Bell M Cratsenburg F 10y New York

1875 NY State Census for Cape Vincent, Jefferson Co., NY:
Adam I Cratsenberg M 58
Wife Esther A Cratsenberg F 56
Son Cassius H Cratsenberg M 18
Dau May Cratsenberg F 15

1880 U.S. Census for Cape Vincent, Jefferson Co., NY:
Adam S. Cratsenberg M 63, b. 1817 New York; lighthouse keeper
Wife Esther A. Cratsenberg F 61, b. 1819 New York
Dau Bell M. Cratsenberg F 20, b. 1860 New York
Son Cassius H. Cratsenberg M 24, b. 1864 NY; sailor

Adam and daughter Belle May Cratsenberg were living with his daughter, Charlotte Marie Hilts and her family in Lyme Township, Chaumont village, Jefferson Co., New York in 1900. Wife Esther passed away in 1889.