Jill Lonita Coit was born Jill Lonita Billiot on June 11, 1943, or possibly in 1944, in Lafitte, Louisiana. She grew up in New Orleans, Louisiana. Jill was of Native American descent. Her childhood appeared quite ordinary, and she did not face any significant trauma during her early years. She was considered popular among her peers at school.

Jill struggled academically and dropped out of high school in 1961. Shortly afterward, she got married for the first time. However, this marriage did not last long, as she filed for divorce within less than a year. After the divorce, she took steps to liquidate the bank accounts she shared with her first husband.

In 1964, Jill married for the second time to a man named Steven Moore. They had a son together, but their marriage also ended quickly when she filed for divorce soon after giving birth. In January 1966, she married William Clark Coit, Jr. while still legally married to Steven Moore. William adopted Jill's son from her previous marriage. Together, they had two children.

Jill's second husband, William Coit Jr., was killed in 1972 under suspicious circumstances. Just before his death, he had filed for divorce from Jill. Even though police suspected her of being involved, they lacked enough evidence to charge her. Following his death, Jill moved to California and involved herself in various financial dealings.

Jill's early adult life consisted of multiple marriages and relationships. She went on to marry several more times, including to a U.S. Marine Corps officer and a schoolteacher. 

Jill Coit was involved in a murder case that drew significant attention. Her third husband, William Clark Coit, Jr., was shot twice in the back on March 29, 1972. This occurred shortly after he filed for divorce from her. Authorities suspected her of the murder, but they were unable to gather enough evidence to bring charges against her. Following his death, Coit checked herself into a mental hospital to avoid further police questioning.

In 1991, Coit married her eighth husband, Gerald Boggs, after meeting him while renovating a bed and breakfast. Their marriage lasted only seven months. Boggs' brother was suspicious of Coit's interest in their finances and hired a private investigator. The investigator found out that Coit had a long history of marriages and scams. Shortly after the annulment of her marriage to Boggs, a murder occurred.

In October 1993, Coit and her new partner, Michael Backus, planned and carried out Boggs' murder. They broke into his home wearing disguises, used a stun gun on him, and killed him with a .25 caliber pistol. After the murder, they fled to Mexico.

Police quickly identified Coit as a suspect after her younger son reported her confession about the murder to them. She was arrested on December 23, 1993 during a trip back from Mexico. During the trial in 1995, evidence showed that she had been planning the murder for some time. She was convicted of first-degree murder and conspiracy to commit first-degree murder, receiving a life sentence without the possibility of parole, plus an additional 47 years for the conspiracy charge. Backus was also convicted and received a life sentence.

Jill Coit is currently incarcerated at the Denver Women's Correctional Facility, having exhausted all her appeals.