Did Joseph Smith marry underage girls?

Joseph Smith’s wives ages ranged from ages 14-58. According to law, the minimum age for a woman to be able to marry was 12 years old. However, the average marriage age for women in the 1800s was around 20-22 years old. On the frontier, the average age for the marriage of a woman would have had more outliers, with more younger women marrying as well as more older women marrying. 

The youngest plural wife of Joseph Smith was Helen Mar Kimball, who was fourteen years old when she was sealed to Smith. Helen’s father was the apostle, Heber C. Kimball. Helen and Heber viewed this marriage as a dynastic sealing. This marriage would tie the Kimballs to the Smiths for eternity. Helen would staunchly defend polygamy later in life and never claimed sexual relations occurred between her and Joseph.