It was in early 2021 that Congressional Democrats passed & President Biden signed the American Rescue Plan Act (ARPA), which among other things dramatically expanded & enhanced the original premium subsidy formula of the Affordable Care Act, finally bringing the financial aid sliding income scale up to the level it should have been in the first place over a decade earlier.
In addition to beefing up the subsidies along the entire 100 - 400% Federal Poverty Level (FPL) income scale, the ARPA also eliminated the much-maligned "Subsidy Cliff" at 400% FPL, wherein a household earning even $1 more than that had all premium subsidies cut off immediately, requiring middle-class families to pay full price for individual market health insurance policies.
Here's what the original ACA premium subsidy formula looked like compared to the current, enhanced subsidy formula:
Mississippi has around ~338,000 residents enrolled in ACA exchange plans, 98% of whom are currently subsidized. I estimate they also have another ~14,000 unsubsidized off-exchange enrollees.
The District of Columbia has around ~15,000 residents enrolled in ACA exchange plans. Unlike most states where nearly all ACA exchange enrollees are subsidized, in DC only around 28% are due to the District having an unusually high income eligibility threshold for Medicaid (210%). DC also has a unique requirement that ACA individual market plans can only be sold on their ACA exchange; I'm assuming perhaps 1,000 off-exchange enrollees regardless but officially I believe this should be pretty much zilch. With net attrition since January, however, it looks like the grand total is actually a bit below 14,000 District-wide.
Montana has around ~77,000 residents enrolled in ACA exchange plans, 89% of whom are currently subsidized. I estimate they also have another ~8,400 unsubsidized off-exchange enrollees.
Missouri has around ~417,000 residents enrolled in ACA exchange plans, 94% of whom are currently subsidized. I estimate they also have another ~3,600 unsubsidized off-exchange enrollees.
Louisiana has around ~293,000 residents enrolled in ACA exchange plans, 96% of whom are currently subsidized. I estimate they also have another ~13,000 unsubsidized off-exchange enrollees.
Maryland has around 247,000 residents enrolled in ACA exchange plans, 76% of whom are currently subsidized. I estimate they also have another ~73,000 unsubsidized off-exchange enrollees.
Michigan has around 531,000 residents enrolled in ACA exchange plans, 91% of whom are currently subsidized. I estimate they also have another ~64,000 unsubsidized off-exchange enrollees.
Massachusetts has around 390,000 residents enrolled in ACA exchange plans, 83% of whom are currently subsidized. I estimate they also have another ~27,000 unsubsidized off-exchange enrollees.
Maine has around 64,000 residents enrolled in ACA exchange plans, 85% of whom are currently subsidized. I estimate they also have another ~4,500 unsubsidized off-exchange enrollees.
Combined, that's around 70,000 people, although it could be somewhat lower due to net enrollment attrition since January.