Jack Mormon is a descriptive term that many view as slang. It can be a confusing term to define or understand because its definition has evolved since it was first used. Initially, Thomas Coke Sharp wrote it as Jack-Mormon. Sharp was the editor of the Warsaw Signal newspaper, and he was strongly opposed to Mormon ideology. He first used this description in 1846, and meant it as a pejorative term for those who were not Mormon but were friendly to Mormons. There is some alternative explanation for the origin of the phrase offered by those who study the Latter Day Saints (LDS) from a historical perspective.
For a long time, Sharp’s definition stood, and a Jack Mormon could be defined as a non-Mormon sympathetic to the views of the LDS or friendly with members of LDS congregations. It wasn’t always pejorative, and often expressed political similarities. Many Democrats especially in the early 20th century, felt treatment of Mormons was unfair and the LDS church was made up of numerous members who would have identified as Democrat in ideology. Thus, this person would be one who shared sympathies with Mormons and similar political views. Interestingly, party association in the US now leans toward Republicanism and a person defined this way today would likely be a Republican.
However, definition of the Jack Mormon began to change and did not stick to Sharp’s initial description. Instead, in the middle 20th century and later, the term became used to describe people who were nominal members of the LDS church but participated in it very little. These people tend to like the Mormon Church and stayed friendly to its members. They usually do not attend services and they may be similar to those people in other Christian sects that only practice their religion at significant holidays like Christmas and Easter.
Yet another definition may be used by LDS members to discuss those Mormons who stray from the traditional behavioral prescriptions of the church. Baptized Mormons who engage in premarital sex, or drink alcohol might be considered Jack Mormons. This is similar to the idea of the Cafeteria Catholic, where those baptized in the Catholic Church tend to pick and choose the ideas of Catholicism that they like and abandon those they don’t. Cafeteria Catholics, like Jack Mormons, might engage in premarital sex, attend church rarely, and ignore other church teachings.