Thanks to the good folks at IPUMS, a project that provides user-friendly census data, this is actually pretty easy to get numbers on. I ran a cross-tab showing percent of the population in Utah that was 14 and under, percent that is 15-64, and percent that is 65+. The former category divided by the middle category creates the “youth dependency ratio,” or the number of youth per working age adult. This is a pretty standard measure that allows us to compare Utah with other countries and areas. I ran the numbers and calculated the ratios for each of the decennial censuses from 1850 on, both for the US and Utah...A few caveats: often censuses have back stories that may affect results (for example, I assume the 1890 Census is missing because a fire destroyed most of those records), so I’m not sure how accurate the 1850 Utah census was given that it was taken shortly after the entry into Utah, but I think overall this paints an accurate picture. Also, later in the 19th century there were more non-Latter-day Saint settlers, so these numbers are “conservative” in the sense that the Latter-day Saint population was even younger once you filter out the heavily adult male miners in Park City. Even so, my image of settlements bursting with children appears to be pretty accurate. (As a side note, sometimes faithful members seem to take the view that polygamy is a great mystery whose divine reasons we should just “put on a shelf” when in my view the both D&C and the Book of Mormon are pretty clear about its purpose: to raise up seed, and raise up seed it certainly did as marriage rates for women were about as high as could be; for example, in her analysis of Manti Utah, Kathryn Daynes could only find one woman in the early Utah years who never married). In 1860 there were more children than working-age adults in Utah. This is incredibly high. As a point of comparison, the only country in the world right now that can say the same is Mali.