diff --git a/pandas/_libs/tslibs/conversion.pxd b/pandas/_libs/tslibs/conversion.pxd
index 623d9f14d646b..2cf75944a8196 100644
--- a/pandas/_libs/tslibs/conversion.pxd
+++ b/pandas/_libs/tslibs/conversion.pxd
@@ -13,11 +13,11 @@ cdef class _TSObject:
         bint fold
 
 
-cdef convert_to_tsobject(object ts, object tz, object unit,
+cdef convert_to_tsobject(object ts, tzinfo tz, object unit,
                          bint dayfirst, bint yearfirst,
                          int32_t nanos=*)
 
-cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
+cdef _TSObject convert_datetime_to_tsobject(datetime ts, tzinfo tz,
                                             int32_t nanos=*)
 
 cdef int64_t get_datetime64_nanos(object val) except? -1
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index ac24dd546d9d3..82a9ad9d3f49b 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -306,7 +306,7 @@ cdef class _TSObject:
         return self.value
 
 
-cdef convert_to_tsobject(object ts, object tz, object unit,
+cdef convert_to_tsobject(object ts, tzinfo tz, object unit,
                          bint dayfirst, bint yearfirst, int32_t nanos=0):
     """
     Extract datetime and int64 from any of:
@@ -325,13 +325,10 @@ cdef convert_to_tsobject(object ts, object tz, object unit,
     cdef:
         _TSObject obj
 
-    if tz is not None:
-        tz = maybe_get_tz(tz)
-
     obj = _TSObject()
 
     if isinstance(ts, str):
-        return convert_str_to_tsobject(ts, tz, unit, dayfirst, yearfirst)
+        return _convert_str_to_tsobject(ts, tz, unit, dayfirst, yearfirst)
 
     if ts is None or ts is NaT:
         obj.value = NPY_NAT
@@ -373,16 +370,16 @@ cdef convert_to_tsobject(object ts, object tz, object unit,
                         f'Timestamp')
 
     if tz is not None:
-        localize_tso(obj, tz)
+        _localize_tso(obj, tz)
 
     if obj.value != NPY_NAT:
-        # check_overflows needs to run after localize_tso
+        # check_overflows needs to run after _localize_tso
         check_dts_bounds(&obj.dts)
         check_overflows(obj)
     return obj
 
 
-cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
+cdef _TSObject convert_datetime_to_tsobject(datetime ts, tzinfo tz,
                                             int32_t nanos=0):
     """
     Convert a datetime (or Timestamp) input `ts`, along with optional timezone
@@ -445,8 +442,8 @@ cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
     return obj
 
 
-cdef _TSObject create_tsobject_tz_using_offset(npy_datetimestruct dts,
-                                               int tzoffset, tzinfo tz=None):
+cdef _TSObject _create_tsobject_tz_using_offset(npy_datetimestruct dts,
+                                                int tzoffset, tzinfo tz=None):
     """
     Convert a datetimestruct `dts`, along with initial timezone offset
     `tzoffset` to a _TSObject (with timezone object `tz` - optional).
@@ -499,9 +496,9 @@ cdef _TSObject create_tsobject_tz_using_offset(npy_datetimestruct dts,
     return obj
 
 
-cdef _TSObject convert_str_to_tsobject(object ts, object tz, object unit,
-                                       bint dayfirst=False,
-                                       bint yearfirst=False):
+cdef _TSObject _convert_str_to_tsobject(object ts, tzinfo tz, object unit,
+                                        bint dayfirst=False,
+                                        bint yearfirst=False):
     """
     Convert a string input `ts`, along with optional timezone object`tz`
     to a _TSObject.
@@ -531,11 +528,6 @@ cdef _TSObject convert_str_to_tsobject(object ts, object tz, object unit,
         int out_local = 0, out_tzoffset = 0
         bint do_parse_datetime_string = False
 
-    if tz is not None:
-        tz = maybe_get_tz(tz)
-
-    assert isinstance(ts, str)
-
     if len(ts) == 0 or ts in nat_strings:
         ts = NaT
     elif ts == 'now':
@@ -556,12 +548,12 @@ cdef _TSObject convert_str_to_tsobject(object ts, object tz, object unit,
             if not string_to_dts_failed:
                 check_dts_bounds(&dts)
                 if out_local == 1:
-                    return create_tsobject_tz_using_offset(dts,
-                                                           out_tzoffset, tz)
+                    return _create_tsobject_tz_using_offset(dts,
+                                                            out_tzoffset, tz)
                 else:
                     ts = dtstruct_to_dt64(&dts)
                     if tz is not None:
-                        # shift for localize_tso
+                        # shift for _localize_tso
                         ts = tz_localize_to_utc(np.array([ts], dtype='i8'), tz,
                                                 ambiguous='raise')[0]
 
@@ -612,7 +604,7 @@ cdef inline check_overflows(_TSObject obj):
 # ----------------------------------------------------------------------
 # Localization
 
-cdef inline void localize_tso(_TSObject obj, tzinfo tz):
+cdef inline void _localize_tso(_TSObject obj, tzinfo tz):
     """
     Given the UTC nanosecond timestamp in obj.value, find the wall-clock
     representation of that timestamp in the given timezone.
diff --git a/pandas/_libs/tslibs/timestamps.pyx b/pandas/_libs/tslibs/timestamps.pyx
index 1328bc8a5175f..e104b722ea119 100644
--- a/pandas/_libs/tslibs/timestamps.pyx
+++ b/pandas/_libs/tslibs/timestamps.pyx
@@ -20,6 +20,7 @@ from cpython.datetime cimport (
     datetime,
     time,
     tzinfo,
+    tzinfo as tzinfo_type,  # alias bc `tzinfo` is a kwarg below
     PyDateTime_Check,
     PyDelta_Check,
     PyTZInfo_Check,
@@ -932,7 +933,7 @@ class Timestamp(_Timestamp):
         second=None,
         microsecond=None,
         nanosecond=None,
-        tzinfo=None,
+        tzinfo_type tzinfo=None,
         *,
         fold=None
     ):
@@ -957,18 +958,17 @@ class Timestamp(_Timestamp):
         #
         # Mixing pydatetime positional and keyword arguments is forbidden!
 
-        cdef _TSObject ts
+        cdef:
+            _TSObject ts
+            tzinfo_type tzobj
 
         _date_attributes = [year, month, day, hour, minute, second,
                             microsecond, nanosecond]
 
         if tzinfo is not None:
-            if not PyTZInfo_Check(tzinfo):
-                # tzinfo must be a datetime.tzinfo object, GH#17690
-                raise TypeError(
-                    f"tzinfo must be a datetime.tzinfo object, not {type(tzinfo)}"
-                )
-            elif tz is not None:
+            # GH#17690 tzinfo must be a datetime.tzinfo object, ensured
+            #  by the cython annotation.
+            if tz is not None:
                 raise ValueError('Can provide at most one of tz, tzinfo')
 
             # User passed tzinfo instead of tz; avoid silently ignoring
@@ -1055,7 +1055,8 @@ class Timestamp(_Timestamp):
             raise ValueError("Cannot pass a datetime or Timestamp with tzinfo with "
                              "the tz parameter. Use tz_convert instead.")
 
-        ts = convert_to_tsobject(ts_input, tz, unit, 0, 0, nanosecond or 0)
+        tzobj = maybe_get_tz(tz)
+        ts = convert_to_tsobject(ts_input, tzobj, unit, 0, 0, nanosecond or 0)
 
         if ts.value == NPY_NAT:
             return NaT
@@ -1378,15 +1379,16 @@ default 'raise'
 
         cdef:
             npy_datetimestruct dts
-            int64_t value, value_tz, offset
-            object _tzinfo, result, k, v
+            int64_t value, value_tz
+            object k, v
             datetime ts_input
+            tzinfo_type tzobj
 
         # set to naive if needed
-        _tzinfo = self.tzinfo
+        tzobj = self.tzinfo
         value = self.value
-        if _tzinfo is not None:
-            value_tz = tz_convert_single(value, _tzinfo, UTC)
+        if tzobj is not None:
+            value_tz = tz_convert_single(value, tzobj, UTC)
             value += value - value_tz
 
         # setup components
@@ -1419,30 +1421,30 @@ default 'raise'
         if nanosecond is not None:
             dts.ps = validate('nanosecond', nanosecond) * 1000
         if tzinfo is not object:
-            _tzinfo = tzinfo
+            tzobj = tzinfo
 
         # reconstruct & check bounds
-        if _tzinfo is not None and treat_tz_as_pytz(_tzinfo):
+        if tzobj is not None and treat_tz_as_pytz(tzobj):
             # replacing across a DST boundary may induce a new tzinfo object
             # see GH#18319
-            ts_input = _tzinfo.localize(datetime(dts.year, dts.month, dts.day,
-                                                 dts.hour, dts.min, dts.sec,
-                                                 dts.us),
-                                        is_dst=not bool(fold))
-            _tzinfo = ts_input.tzinfo
+            ts_input = tzobj.localize(datetime(dts.year, dts.month, dts.day,
+                                               dts.hour, dts.min, dts.sec,
+                                               dts.us),
+                                      is_dst=not bool(fold))
+            tzobj = ts_input.tzinfo
         else:
             kwargs = {'year': dts.year, 'month': dts.month, 'day': dts.day,
                       'hour': dts.hour, 'minute': dts.min, 'second': dts.sec,
-                      'microsecond': dts.us, 'tzinfo': _tzinfo,
+                      'microsecond': dts.us, 'tzinfo': tzobj,
                       'fold': fold}
             ts_input = datetime(**kwargs)
 
-        ts = convert_datetime_to_tsobject(ts_input, _tzinfo)
+        ts = convert_datetime_to_tsobject(ts_input, tzobj)
         value = ts.value + (dts.ps // 1000)
         if value != NPY_NAT:
             check_dts_bounds(&dts)
 
-        return create_timestamp_from_ts(value, dts, _tzinfo, self.freq, fold)
+        return create_timestamp_from_ts(value, dts, tzobj, self.freq, fold)
 
     def to_julian_date(self) -> np.float64:
         """
diff --git a/pandas/tests/scalar/timestamp/test_constructors.py b/pandas/tests/scalar/timestamp/test_constructors.py
index 770753f42a4c8..316a299ba1cbb 100644
--- a/pandas/tests/scalar/timestamp/test_constructors.py
+++ b/pandas/tests/scalar/timestamp/test_constructors.py
@@ -174,7 +174,10 @@ def test_constructor_invalid(self):
 
     def test_constructor_invalid_tz(self):
         # GH#17690
-        msg = "must be a datetime.tzinfo"
+        msg = (
+            "Argument 'tzinfo' has incorrect type "
+            r"\(expected datetime.tzinfo, got str\)"
+        )
         with pytest.raises(TypeError, match=msg):
             Timestamp("2017-10-22", tzinfo="US/Eastern")