Regarding his Howard County personal slaveholdings: From the 1924 Johns Hopkins study entitled Slavery In Missouri 1804-1865 -- In 1856 "...In the adjoining county of Howard William Swinney paid taxes on 86 slaves valued at $44,800 and on 1369 acres of land....George Cason was second with 52 negroes, and John R. White third with 46."
Regarding his slave trading activities from the same study: "....There was at least one permanent firm of dealers in St. Joseph in 1856. John Doy asserts that while he was imprisoned in St. Joseph many negroes were shipped from there to Bernard Lynch, Corbin Thompson, and other large St. Louis buyers. Columbia and Marshall were regularly visited, and Platte City had quite a thriving trade. John R. White of Howard County was a wealthy planter of good repute who dealt in slaves. He lived on a farm of 1053 acres and was taxed with 46 negroes in 1856. The slave-trader, like the stock dealer, undoubtedly plied his trade wherever he could obtain his commodity...."
Regarding White's holdings for this study, just the Howard County tax records were reviewed. No doubt an inquiry into surrounding counties and regional records would have revealed his more extensive holdings.