Helen Mar Kimball recalls hearing that Joseph preached on plural marriage publicly in 1841.
Helen Mar Kimball, Plural Marriage, As Taught by the Prophet Joseph (Salt Lake City, UT: Juvenile Instructor Office, 1882), 11–12
A revelation upon the eternity of the marriage covenant was given to the Prophet long before the year 1843, as he asserted, and I am pleased to be able to testify to his son that on a certain Sabbath morning, previous to the return of the Apostles from Europe, in 1841, he astonished his hearers by preaching on the restoration of all things, and said that as it was anciently with Abraham, Isaac and Jacob, so it would be again, etc. He spoke so plainly that his wife, Emma, as well as others were quite excited over it. Seeing the effect his sermon had upon them, he consoled them in the afternoon by saying that the time of which he had spoken might be further off than he anticipated, at all events the Lord would assist them to understand and perform His will in the matter if they were faithful. My mother was present and heard him deliver both discourses, and I recollect hearing her with others of the sisters express their astonishment at the things they heard that day.