
In 1840, Lincoln became engaged to Mary Todd, a daughter of Robert Smith Todd. Lincoln's father-in-law was a wealthy slave owner in Lexington, Kentucky. The future President and First Lady had met in Lincoln's home of Springfield, Illinois, in December 1839. The became engaged a year later. A wedding had been planned for January 1, 1841, but it was called off at Lincoln's request. The couple reconciled and were married on November 4, 1842, in the Springfield mansion that was the home of Mary's sister. In 1844, the couple bought a house in Springfield near Lincoln's law office.
The Lincolns had four children, all sons. Only one would live past the age of 18. That was Robert Todd Lincoln who was born in 1843, and who had a distinguished career as a cabinet member, diplomat and business man. Lincoln's second son Edward Baker Lincoln, called Eddie by his parents, was born in 1846. He was named after Lincoln's friend Edward Dickinson Baker, a fellow Illinois lawyer and politician. Eddie was described by his parents as a very tender-hearted and kindly natured child. Eddie died a month before his fourth birthday. The cause of death was listed as "chronic consumption", a contemporary term for tuberculosis, though later medical historians have theorized that the cause of Eddie's death might have actually been thyroid cancer. Eddie's funeral was held at the Lincoln home and was officiated by the pastor of the First Presbyterian Church. He was interred at Hutchinson's Cemetery in Springfield, Illinois, but his remains would later be relocated to his father's resting place. Both of his parents were devastated, and this was likely a contributing factor in the severe depression that both of Eddie's parents would experience during their lifetime.
The Lincoln's third son was William Wallace Lincoln, known as "Willie". He was born on December 21, 1850 and was named after Mary's brother-in-law, Dr. William Wallace. Willie and his younger brother Thomas, known as "Tad" were remembered to be "notorious hellions" by their father's Springfield law partner William Herndon, who said that their father appeared oblivious to their hijinx. Herndon was quoted as saying: "I have felt many and many a time that I wanted to wring their little necks, and yet out of respect for Lincoln I kept my mouth shut. Lincoln did not note what his children were doing or had done."
When Lincoln became President of the United States, Willie and Tad moved into the White House. Willie and Tad became ill in early 1862. Their illness was believed to be typhoid fever. Typhoid is a bacterial infection caused by a specific type of Salmonella. Symptoms may vary from mild to severe, and usually begin 6 to 30 days after exposure. Often there is a gradual onset of a high fever over several days. The fever is commonly accompanied by weakness, abdominal pain, constipation, headaches, and mild vomiting. Some people develop a skin rash with rose colored spots.
Tad appeared to have a minor case of the illness, but not so for Willie. As his illness persisted, he gradually weakened and his parents spent much time at his bedside. His condition worsened and Willie died on February 20. The Lincolns were once again devastated at experiencing the loss of a child. Lincoln said of Willie's death: "My poor boy. He was too good for this earth. God has called him home. I know that he is much better off in heaven, but then we loved him so much. It is hard, hard to have him die!"
After Willie's funeral, Lincoln shut himself in a room and wept. Mary Lincoln remained in bed for three weeks and was unable to attend Willie's funeral or look after Tad. Abraham Lincoln spent time caring for and comforting Tad, whose illness now worsened.
Willie was interred at Oak Hill Cemetery in Georgetown. After his father's assassination in 1865, he was re-interred at Oak Ridge Cemetery in Springfield, Illinois, first in a temporary tomb and in 1871 in a state tomb alongside his father and his brother Eddie. Tad and Mary Todd Lincoln were also later placed in the crypt of the Lincoln Tomb.
The Lincoln's youngest son, Thomas "Tad" Lincoln, was born on April 4, 1853. He would survive his father, but would not live to see his 19th birthday. He died at age 18 on July 16, 1871. The cause of death has been cited to be for different reasons, including tuberculosis, pleurasy, pneumonia, or congestive heart failure.

The deaths of their sons had profound effects on both parents. Abraham suffered from "melancholy," a condition later referred to as clinical depression. For the remainder of her life Mary Lincoln also struggled with the stresses of losing her husband and sons. Her son Robert had her temporarily committed to a mental health asylum in 1875.