Joseph, as editor of Elders' Journal affirms in 1838 that Mormons do not believe in polygamy.
Joseph Smith, ed., Elders' Journal 1, no. 3 (July 1838): 43
Question 7th. Do the Mormons believe in having more wives than one.
Answer. No, not at the same time. But they believe, that if their companion dies, they have a right to marry again. But we do disapprove of the custom which has gained in the world, and has been practised among us, to our great mortification, of marrying in five or six weeks, or even in two or three months after the death of their companion.
We believe that due respect ought to be had, to the memory of the dead, and the feelings of both friends and children.