Sorry, but this is faulty -- even by the census taken by Utah Mormons, per Lds "apostle" John Widtsoe.
According to the Changing World of Mormonism, pp. 224-225: [LDS} "Apostle” John A. Widtsoe, who was born during the polygamy years (early 1870s) stated:
’We do not understand why the Lord commanded the practice of plural marriage.’ (Evidences and Reconciliations, 1960, p.393). One of the most popular explanations is that the church practiced polygamy because there was a surplus of women. The truth is, however, that there were less women than men. Apostle Widtsoe admitted that there was no surplus of women”: 'The implied assumption in this theory, that there have been more female than male members in the Church, is not supported by existing evidence. On the contrary, there seems always to have been more males than females in the Church.’.. The United States census records from 1850 to 1940, and all available Church records, uniformly show a preponderance of males in Utah, and in the Church. Indeed, the excess in Utah has usually been larger than for the whole United States, ... there was no surplus of women'” (Widtsoe, Evidences and Reconciliations, 1960, pp.390-92," as cited in Changing World, pp. 224-225).
“The implied assumption in this theory, that there have been more female than male members in the Church, is not supported by existing evidence. On the contrary, there seems always to have been more males than females in the Church.’”
Makes sense, since adopting polygamy would tend to attract more men to a church than women.