What was the population of Myaamia (Miami Indian) villages pre-contact with Europeans?
The short answer is at least 10,000 to 12,000. However, the longer answer is trickier.
It is extremely difficult to estimate Miami Indian population numbers prior to the period of European contact for at least three main reasons. First, it is extremely difficult to connect the archaeological record of villages from the late 1400s directly to Miami speaking communities. While scholars can estimate the populations of these villages, they don’t know for sure which villages were Miami. Second, waves of disease epidemics swept through North America in the 1500s. This was over 100 years before our ancestors first met the French. Mortality rates from these “virgin soil” epidemics of small pox and measles ran anywhere from 50-90%. These cataclysmic death rates threw our ancestors villages into chaos. Third, waves of warfare – often called “the Beaver Wars” – caused additional disruption and chaos. It was in this context of disruption that the our ancestors and the French first encountered each other (to read more about this period follow this link). It was in these chaotic moments that the French made their first estimates of Miami population.
Because of these uncertainties, many historians prefer to set up ranges for their estimates. The highest estimates of around 25,000 are based on early French reports of village populations. This number is likely inflated by a combination of wishful thinking on the part of the French, and their early inability to differentiate Myaamia people from Meskwaki and Inoka (Illinois).
More conservative scholars estimate a much lower pre-contact population of 4,000. This number uses the drastically diminished populations of the late 1790s and early 1800s to estimate the pre-contact population. These estimates fail to account for the extreme decrease in population, which followed the arrival of European diseases in the 1500s and the increased violence of the 1600s.
I tend to support a middle ground estimate of 10,000-12,000. This population was split up among 6 large villages and many smaller communities. This population crashed in the 1500s and 1600s and then recovered over the 1700s.
By the 1780s, Myaamia population was around 2,000 and by the time of our first forced removal in 1846 our population was below 600 individuals. However, a part of this decline resulted from the political separation of the Waayaahtanwa (Wea) and Peeyankihšia (Piankashaw) from the rest of their Miami-speaking relatives in the Wabash River Valley. Over the 20th century, Myaamia population began another process of recovery. As of early 2017, the Miami Tribe of Oklahoma numbers over 5,000. There are likely another 4,000-6,000 individuals of Myaamia descent who are not citizens of the Miami Tribe of Oklahoma.
 Anson cites the French references of 24,000, but asserts a much lower population of 4,500. Though he cautions that this estimate may include the Peoria. Bert Anson, The Miami Indians, 1st ed. (Norman: University of Oklahoma Press, 1970), 32. White gives the following for early population counts among the Myaamia: “The Miami fell dramatically in number; their total warrior strength dropped from 1,400 or 1,600 in 1718, to 600 or 700 in 1733, to about 550 in 1736.” If one uses the typical 1×4 calculation, this would give a population of ~6,400 in 1718 and ~2,200 in 1736. Richard White, The Middle Ground: Indians, Empires, and Republics in the Great Lakes Region, 1650-1815, Cambridge Studies in North American Indian History. (Cambridge; New York: Cambridge University Press, 1991), 145.
 Carter posits that the Miami population may have been as large as 10,000 in the 1680s, though he believes this number is an overestimate. By the 1750’s he believes the population was around 2,000. Harvey Lewis Carter, The Life and Times of Little Turtle: First Sagamore of the Wabash (Urbana: University of Illinois Press, 1987), 27. Rafert provides his own estimates, see Stewart Rafert, The Miami Indians of Indiana: A Persistent People, 1654-1994 (Indianapolis, Ind.: Indiana Historical Society, 1996), 8.
 In 1763, William Johnson estimated the Myaamia of the upper Wabash to have 230 men of arms bearing age, the Peeyankihšia 100, and the Waayaahtanwa 200. However, calculating a village population off of these numbers is also a challenge. The historian, Harvey Lewis Carter recommends an estimate of one adult woman and two children for each adult male. In 1824, Trowbridge was told that 1/3 of Myaamia women did not have children, but that remaining 2/3’s had on average 6 children each. However, some women had as many as 13 children. Charles C. Trowbridge and W. Vernon Kinietz, Meearmeear Traditions (Ann Arbor [Mich.]: University of Michigan Press, 1938), 46. Sinclair’s letters and reports from the 1846 forced removal lists the total Myaamia population as 555 of which 112 were men over 18 (a ratio of 1 to 5). See p. 22 of removal booklet – myaamiaki aancihsaaciki – http://myaamiacenter.org/wp-content/uploads/2013/02/myaamia_removal.pdf