A section of U.S. Route 209 outside Kingston also was used for a confrontation between Dominick and Thomas in the first episode; the road was closed for two days in both directions for filming. On Rotten Tomatoes, the miniseries holds an approval rating of 76% based on 50 reviews, with an average rating of 6.85/10. The website's critical consensus reads, ""I Know This Much is True" relentlessly grim plotting makes it a difficult watch, but the strength of Mark Ruffalo's dual performances is enough to make it a dark tale worth tuning into." On Metacritic, it has a weighted average score of 66 out of 100 based on 25 reviews, indicating "generally favorable reviews". Writing for "The A. V. Club", Ines Bellina rated the series a B–, praising Ruffalo's performance but criticizing it for not being enjoyable to watch and summing it up as "an uneven journey, overwhelming in its self-indulgent trauma... [but] Against all odds, it ends on a more heartfelt and hopeful note than the preceding six hours would lead you to believe."