Shortly after Louisa returned to the Big House in the spring of 1878, Charles married his third wife, Agnes Mary Willmott. In spite of persecution, Charles still felt that as a Bishop it was his responsibility to live the law of plural marriage to the best of his ability. Family tradition indicates that neither Louisa nor Esther knew Charles was going to marry Agnes until he brought her to the Big House to live. If this story is true, it shows the trust and confidence Louisa and Esther had in Charles as they accepted his third wife. Agnes and Charles were married by Elder Wilford Woodruff in the Endowment House in Salt Lake City on April 11, 1878. Agnes, whom he met in Coalville, was a beautiful girl, very frail and delicate. She was 20 years old and Charles was 50.

Agnes was born in Bassingbourn, Cambridgeshire, England, on March 3, 1858. Her parents were Edward Willmott and Ann Noble. She attended public school until she was 12 years of age. When she was nearly fifteen she went to London to work for a family as a nurse girl. She was working as a parlor maid with a wealthy family when she heard the message of the Mormon elders. She accepted the gospel and was baptized September 3, 1876, when she was 18 years old. Her mother and an older sister were baptized a few months before she joined the Church. They immigrated to Utah in 1876.

Agnes and her younger sister Eliza came to Zion the following year. They crossed the ocean on the Steamship Idaho which left Liverpool, England, October 17, 1877, with 150 saints, including 12 returning elders. In charge of the group from England to Salt Lake City was Elder William Paxman. Elder Paxman was sea sick the entire journey. A number of excellent singers in the company helped make the journey enjoyable. The ship arrived at New York October 29th. From there the company traveled by train to Salt Lake City arriving November 7, 1877. Agnes and Eliza debarked from the train in Echo, Utah, where it is believed she was met by family or friends and taken to Coalville. Her father and oldest brother, John, never did accept the gospel, but her brother, George, came to Utah and was baptized at Henefer. Her brothers and sisters were John, Elizabeth, George, Eliza and Jane.