Matthew Poole and continuators on 2 Samuel 24:9

9 And Joab gave up the sum of the number of the people unto the king: and there were in Israel eight hundred thousand valiant men that drew the sword; and the men of Judah were five hundred thousand men.

Obj. In 1 Chron. 21. 5. They are Numbred 1100 thousand. Answ. The sum here Expressed, is onely of such as were not in the ordinary and settled Militia waiting upon the King, which being 24000 for every Month, as is largely related, 1 Chron. 27. amounts to 288 Thousand, which either with their several Commanders, or with the Soldiers placed in several Garisons, might very well make up 300 Thousand. Or, 288 Thousand may pass in such accounts for 300 Thousand; it being frequent in such great Sums to neglect a smaller number. But in the Book of the Chronicles, which was to gather up the Fragments omitted in the former Books, both sorts are put together, and so they amount to 1100 Thousand.

In 1 Chron. 21. 5. but 470 Thousand. Answ. Either, 1. they were exactly no more, but are called 500 Thousand in a round sum, as is usual in Scripture, and other Authors. Or, 2. the Garison-Soldiers, and such as were imployed in other Services about the King are here included, which are there excluded. Or, 3. They were 500 Thousand when Ioab gave up the Number to the King; though presently after that, they were but 470 Thousand, 30000 being slain by the Plague, in the Tribe of Iudah; which being David's own Tribe, it was but just and fit it should suffer more than the rest for this Sin. And though it be true, that Ioab gave up the Sum before the Plague begun, yet the Sacred Penman of the Book of Chronicles, thought fit to make a defalcation of them who had been swept away by the Plague, that the Judgment of God therein might be observed. Or, 4. there are included here the 30000 which belonged to the 30 Colonels mentioned Chap. 23. who are Excluded 1 Chron. 21. although it be questionable, whether those were all of the Tribe of Iudah.