diff --git a/mypyc/lib-rt/CPy.h b/mypyc/lib-rt/CPy.h
index 1f0cf4dd63d6..5288e05efc3e 100644
--- a/mypyc/lib-rt/CPy.h
+++ b/mypyc/lib-rt/CPy.h
@@ -752,6 +752,8 @@ bool CPyStr_IsTrue(PyObject *obj);
 Py_ssize_t CPyStr_Size_size_t(PyObject *str);
 PyObject *CPy_Decode(PyObject *obj, PyObject *encoding, PyObject *errors);
 PyObject *CPy_Encode(PyObject *obj, PyObject *encoding, PyObject *errors);
+Py_ssize_t CPyStr_Count(PyObject *unicode, PyObject *substring, CPyTagged start);
+Py_ssize_t CPyStr_CountFull(PyObject *unicode, PyObject *substring, CPyTagged start, CPyTagged end);
 CPyTagged CPyStr_Ord(PyObject *obj);
 
 
diff --git a/mypyc/lib-rt/str_ops.c b/mypyc/lib-rt/str_ops.c
index 49fcbb8c6876..210172c57497 100644
--- a/mypyc/lib-rt/str_ops.c
+++ b/mypyc/lib-rt/str_ops.c
@@ -511,6 +511,30 @@ PyObject *CPy_Encode(PyObject *obj, PyObject *encoding, PyObject *errors) {
     }
 }
 
+Py_ssize_t CPyStr_Count(PyObject *unicode, PyObject *substring, CPyTagged start) {
+    Py_ssize_t temp_start = CPyTagged_AsSsize_t(start);
+    if (temp_start == -1 && PyErr_Occurred()) {
+        PyErr_SetString(PyExc_OverflowError, CPYTHON_LARGE_INT_ERRMSG);
+        return -1;
+    }
+    Py_ssize_t end = PyUnicode_GET_LENGTH(unicode);
+    return PyUnicode_Count(unicode, substring, temp_start, end);
+}
+
+Py_ssize_t CPyStr_CountFull(PyObject *unicode, PyObject *substring, CPyTagged start, CPyTagged end) {
+    Py_ssize_t temp_start = CPyTagged_AsSsize_t(start);
+    if (temp_start == -1 && PyErr_Occurred()) {
+        PyErr_SetString(PyExc_OverflowError, CPYTHON_LARGE_INT_ERRMSG);
+        return -1;
+    }
+    Py_ssize_t temp_end = CPyTagged_AsSsize_t(end);
+    if (temp_end == -1 && PyErr_Occurred()) {
+        PyErr_SetString(PyExc_OverflowError, CPYTHON_LARGE_INT_ERRMSG);
+        return -1;
+    }
+    return PyUnicode_Count(unicode, substring, temp_start, temp_end);
+}
+
 
 CPyTagged CPyStr_Ord(PyObject *obj) {
     Py_ssize_t s = PyUnicode_GET_LENGTH(obj);
diff --git a/mypyc/primitives/str_ops.py b/mypyc/primitives/str_ops.py
index ded339b9672c..9d46da9c3514 100644
--- a/mypyc/primitives/str_ops.py
+++ b/mypyc/primitives/str_ops.py
@@ -277,6 +277,34 @@
     error_kind=ERR_MAGIC,
 )
 
+# str.count(substring)
+method_op(
+    name="count",
+    arg_types=[str_rprimitive, str_rprimitive],
+    return_type=c_pyssize_t_rprimitive,
+    c_function_name="CPyStr_Count",
+    error_kind=ERR_NEG_INT,
+    extra_int_constants=[(0, c_pyssize_t_rprimitive)],
+)
+
+# str.count(substring, start)
+method_op(
+    name="count",
+    arg_types=[str_rprimitive, str_rprimitive, int_rprimitive],
+    return_type=c_pyssize_t_rprimitive,
+    c_function_name="CPyStr_Count",
+    error_kind=ERR_NEG_INT,
+)
+
+# str.count(substring, start, end)
+method_op(
+    name="count",
+    arg_types=[str_rprimitive, str_rprimitive, int_rprimitive, int_rprimitive],
+    return_type=c_pyssize_t_rprimitive,
+    c_function_name="CPyStr_CountFull",
+    error_kind=ERR_NEG_INT,
+)
+
 # str.replace(old, new)
 method_op(
     name="replace",
diff --git a/mypyc/test-data/irbuild-str.test b/mypyc/test-data/irbuild-str.test
index ad495dddcb15..2bf77a6cb556 100644
--- a/mypyc/test-data/irbuild-str.test
+++ b/mypyc/test-data/irbuild-str.test
@@ -504,3 +504,61 @@ L0:
     r7 = CPyStr_Strip(s, 0)
     r8 = CPyStr_RStrip(s, 0)
     return 1
+
+[case testCountAll]
+def do_count(s: str) -> int:
+    return s.count("x")  # type: ignore [attr-defined]
+[out]
+def do_count(s):
+    s, r0 :: str
+    r1 :: native_int
+    r2 :: bit
+    r3 :: object
+    r4 :: int
+L0:
+    r0 = 'x'
+    r1 = CPyStr_Count(s, r0, 0)
+    r2 = r1 >= 0 :: signed
+    r3 = box(native_int, r1)
+    r4 = unbox(int, r3)
+    return r4
+
+[case testCountStart]
+def do_count(s: str, start: int) -> int:
+    return s.count("x", start)  # type: ignore [attr-defined]
+[out]
+def do_count(s, start):
+    s :: str
+    start :: int
+    r0 :: str
+    r1 :: native_int
+    r2 :: bit
+    r3 :: object
+    r4 :: int
+L0:
+    r0 = 'x'
+    r1 = CPyStr_Count(s, r0, start)
+    r2 = r1 >= 0 :: signed
+    r3 = box(native_int, r1)
+    r4 = unbox(int, r3)
+    return r4
+
+[case testCountStartEnd]
+def do_count(s: str, start: int, end: int) -> int:
+    return s.count("x", start, end)  # type: ignore [attr-defined]
+[out]
+def do_count(s, start, end):
+    s :: str
+    start, end :: int
+    r0 :: str
+    r1 :: native_int
+    r2 :: bit
+    r3 :: object
+    r4 :: int
+L0:
+    r0 = 'x'
+    r1 = CPyStr_CountFull(s, r0, start, end)
+    r2 = r1 >= 0 :: signed
+    r3 = box(native_int, r1)
+    r4 = unbox(int, r3)
+    return r4
diff --git a/mypyc/test-data/run-strings.test b/mypyc/test-data/run-strings.test
index 9183b45b036a..074e56f9068a 100644
--- a/mypyc/test-data/run-strings.test
+++ b/mypyc/test-data/run-strings.test
@@ -815,3 +815,94 @@ def test_unicode_range() -> None:
     assert "\u2029 \U0010AAAA\U00104444B\u205F ".strip() == "\U0010AAAA\U00104444B"
     assert " \u3000\u205F ".strip() == ""
     assert "\u2029 \U00102865\u205F ".rstrip() == "\u2029 \U00102865"
+
+[case testCount]
+# mypy: disable-error-code="attr-defined"
+def test_count() -> None:
+    string = "abcbcb"
+    assert string.count("a") == 1
+    assert string.count("b") == 3
+    assert string.count("c") == 2
+def test_count_start() -> None:
+    string = "abcbcb"
+    assert string.count("a", 2) == string.count("a", -4) == 0, (string.count("a", 2), string.count("a", -4))
+    assert string.count("b", 2) == string.count("b", -4) == 2, (string.count("b", 2), string.count("b", -4))
+    assert string.count("c", 2) == string.count("c", -4) == 2, (string.count("c", 2), string.count("c", -4))
+    # out of bounds
+    assert string.count("a", 8) == 0
+    assert string.count("a", -8) == 1
+    assert string.count("b", 8) == 0
+    assert string.count("b", -8) == 3
+    assert string.count("c", 8) == 0
+    assert string.count("c", -8) == 2
+def test_count_start_end() -> None:
+    string = "abcbcb"
+    assert string.count("a", 0, 4) == 1, string.count("a", 0, 4)
+    assert string.count("b", 0, 4) == 2, string.count("b", 0, 4)
+    assert string.count("c", 0, 4) == 1, string.count("c", 0, 4)
+def test_count_multi() -> None:
+    string = "aaabbbcccbbbcccbbb"
+    assert string.count("aaa") == 1, string.count("aaa")
+    assert string.count("bbb") == 3, string.count("bbb")
+    assert string.count("ccc") == 2, string.count("ccc")
+def test_count_multi_start() -> None:
+    string = "aaabbbcccbbbcccbbb"
+    assert string.count("aaa", 6) == string.count("aaa", -12) == 0, (string.count("aaa", 6), string.count("aaa", -12))
+    assert string.count("bbb", 6) == string.count("bbb", -12) == 2, (string.count("bbb", 6), string.count("bbb", -12))
+    assert string.count("ccc", 6) == string.count("ccc", -12) == 2, (string.count("ccc", 6), string.count("ccc", -12))
+    # out of bounds
+    assert string.count("aaa", 20) == 0
+    assert string.count("aaa", -20) == 1
+    assert string.count("bbb", 20) == 0
+    assert string.count("bbb", -20) == 3
+    assert string.count("ccc", 20) == 0
+    assert string.count("ccc", -20) == 2
+def test_count_multi_start_end() -> None:
+    string = "aaabbbcccbbbcccbbb"
+    assert string.count("aaa", 0, 12) == 1, string.count("aaa", 0, 12)
+    assert string.count("bbb", 0, 12) == 2, string.count("bbb", 0, 12)
+    assert string.count("ccc", 0, 12) == 1, string.count("ccc", 0, 12)
+def test_count_emoji() -> None:
+    string = "😴🚀ñ🚀ñ🚀"
+    assert string.count("😴") == 1, string.count("😴")
+    assert string.count("🚀") == 3, string.count("🚀")
+    assert string.count("ñ") == 2, string.count("ñ")
+def test_count_start_emoji() -> None:
+    string = "😴🚀ñ🚀ñ🚀"
+    assert string.count("😴", 2) == string.count("😴", -4) == 0, (string.count("😴", 2), string.count("😴", -4))
+    assert string.count("🚀", 2) == string.count("🚀", -4) == 2, (string.count("🚀", 2), string.count("🚀", -4))
+    assert string.count("ñ", 2) == string.count("ñ", -4) == 2, (string.count("ñ", 2), string.count("ñ", -4))
+    # Out of bounds
+    assert string.count("😴", 8) == 0, string.count("😴", 8)
+    assert string.count("😴", -8) == 1, string.count("😴", -8)
+    assert string.count("🚀", 8) == 0, string.count("🚀", 8)
+    assert string.count("🚀", -8) == 3, string.count("🚀", -8)
+    assert string.count("ñ", 8) == 0, string.count("ñ", 8)
+    assert string.count("ñ", -8) == 2, string.count("ñ", -8)
+def test_count_start_end_emoji() -> None:
+    string = "😴🚀ñ🚀ñ🚀"
+    assert string.count("😴", 0, 4) == 1, string.count("😴", 0, 4)
+    assert string.count("🚀", 0, 4) == 2, string.count("🚀", 0, 4)
+    assert string.count("ñ", 0, 4) == 1, string.count("ñ", 0, 4)
+def test_count_multi_emoji() -> None:
+    string = "😴😴😴🚀🚀🚀ñññ🚀🚀🚀ñññ🚀🚀🚀"
+    assert string.count("😴😴😴") == 1, string.count("😴😴😴")
+    assert string.count("🚀🚀🚀") == 3, string.count("🚀🚀🚀")
+    assert string.count("ñññ") == 2, string.count("ñññ")
+def test_count_multi_start_emoji() -> None:
+    string = "😴😴😴🚀🚀🚀ñññ🚀🚀🚀ñññ🚀🚀🚀"
+    assert string.count("😴😴😴", 6) == string.count("😴😴😴", -12) == 0, (string.count("😴😴😴", 6), string.count("😴😴😴", -12))
+    assert string.count("🚀🚀🚀", 6) == string.count("🚀🚀🚀", -12) == 2, (string.count("🚀🚀🚀", 6), string.count("🚀🚀🚀", -12))
+    assert string.count("ñññ", 6) == string.count("ñññ", -12) == 2, (string.count("ñññ", 6), string.count("ñññ", -12))
+    # Out of bounds
+    assert string.count("😴😴😴", 20) == 0, string.count("😴😴😴", 20)
+    assert string.count("😴😴😴", -20) == 1, string.count("😴😴😴", -20)
+    assert string.count("🚀🚀🚀", 20) == 0, string.count("🚀🚀🚀", 20)
+    assert string.count("🚀🚀🚀", -20) == 3, string.count("🚀🚀🚀", -20)
+    assert string.count("ñññ", 20) == 0, string.count("ñññ", 20)
+    assert string.count("ñññ", -20) == 2, string.count("ñññ", -20)
+def test_count_multi_start_end_emoji() -> None:
+    string = "😴😴😴🚀🚀🚀ñññ🚀🚀🚀ñññ🚀🚀🚀"
+    assert string.count("😴😴😴", 0, 12) == 1, string.count("😴😴😴", 0, 12)
+    assert string.count("🚀🚀🚀", 0, 12) == 2, string.count("🚀🚀🚀", 0, 12)
+    assert string.count("ñññ", 0, 12) == 1, string.count("ñññ", 0, 12)