diff --git a/changelog.d/casetext-known-dead.changed.md b/changelog.d/casetext-known-dead.changed.md
new file mode 100644
index 00000000000..4eb5cf2f5fc
--- /dev/null
+++ b/changelog.d/casetext-known-dead.changed.md
@@ -0,0 +1 @@
+List casetext.com in the known-dead reference URL guard so its links cannot return.
diff --git a/policyengine_us/tests/code_health/known_dead_reference_urls/casetext_com.toml b/policyengine_us/tests/code_health/known_dead_reference_urls/casetext_com.toml
new file mode 100644
index 00000000000..b18fa694ce5
--- /dev/null
+++ b/policyengine_us/tests/code_health/known_dead_reference_urls/casetext_com.toml
@@ -0,0 +1,16 @@
+# Dead casetext.com reference URLs.
+# casetext.com shut down. Statute, regulation and case pages, and every other
+# path tried except the root, return HTTP 410 Gone to a GET request with a
+# "This service is no longer available" notice; the root redirects to a
+# Thomson Reuters product page with no legal text. #9627 removed all 197
+# links (55 distinct URLs).
+# See test_known_dead_reference_urls.py for the format.
+
+[[dead]]
+prefix = "https://casetext.com/"
+verified = "2026-10-06"
+replacement = """\
+the same section on the official legislature or code site, or \
+law.justia.com where the state has no free official per-section code; \
+Cornell LII (law.cornell.edu/regulations/<state>/...) for state \
+regulations without a usable official deep link."""
diff --git a/policyengine_us/tests/code_health/test_known_dead_reference_urls.py b/policyengine_us/tests/code_health/test_known_dead_reference_urls.py
index ae4fae3d7cc..aa2483f3ab5 100644
--- a/policyengine_us/tests/code_health/test_known_dead_reference_urls.py
+++ b/policyengine_us/tests/code_health/test_known_dead_reference_urls.py
@@ -235,6 +235,11 @@ def test_known_dead_url_entries_are_well_formed():
         "# https://www.tax.ny.gov/pdf/current_forms/it/it558i.pdf",
         "href: HTTPS://WWW.TAX.NY.GOV/pit/child-earned-payments.htm#amount",
         '"[IT-201-I](https://www.tax.ny.gov/pdf/2023/printable-pdfs/inc/it201i-2023.pdf)"',
+        # casetext.com is listed as a whole host: statute, regulation and case
+        # pages are all flagged.
+        "# http://www.casetext.com/statute/kansas-statutes/chapter-79-taxation/article-32-income-tax/section-79-32121-kansas-exemption-for-an-individual",
+        "href: https://casetext.com/regulation/new-jersey-administrative-code/title-18-treasury-taxation/chapter-35-new-jersey-gross-income-tax/subchapter-2-exclusions-and-deductions/section-1835-29-medical-expenses-deduction",
+        '"[Marbury v. Madison](https://casetext.com/case/marbury-v-madison)"',
     ],
 )
 def test_dead_urls_are_flagged(text):
@@ -252,6 +257,7 @@ def test_dead_urls_are_flagged(text):
         "href: https://www.tax.ny.gov/pdf/current_forms/it/it201i.pdf#page=25",
         "href: https://www.tax.ny.gov/pdf/current_forms/it/it558i.pdfx",
         "href: https://www.tax.ny.gov/pit/inflation-refund-checks-faq.htm",
+        "href: https://web.archive.org/web/2023/https://casetext.com/case/marbury-v-madison",
     ],
 )
 def test_archived_and_live_urls_are_not_flagged(text):