diff --git a/pandas/plotting/_matplotlib/converter.py b/pandas/plotting/_matplotlib/converter.py
index 214a67690d695..3db7c38eced65 100644
--- a/pandas/plotting/_matplotlib/converter.py
+++ b/pandas/plotting/_matplotlib/converter.py
@@ -2,7 +2,7 @@
 import datetime as pydt
 from datetime import datetime, timedelta, tzinfo
 import functools
-from typing import Optional, Tuple
+from typing import Any, List, Optional, Tuple
 
 from dateutil.relativedelta import relativedelta
 import matplotlib.dates as dates
@@ -144,7 +144,7 @@ def convert(value, unit, axis):
         return value
 
     @staticmethod
-    def axisinfo(unit, axis):
+    def axisinfo(unit, axis) -> Optional[units.AxisInfo]:
         if unit != "time":
             return None
 
@@ -294,7 +294,7 @@ def try_parse(values):
         return values
 
     @staticmethod
-    def axisinfo(unit, axis):
+    def axisinfo(unit: Optional[tzinfo], axis) -> units.AxisInfo:
         """
         Return the :class:`~matplotlib.units.AxisInfo` for *unit*.
 
@@ -473,7 +473,7 @@ def _get_default_annual_spacing(nyears) -> Tuple[int, int]:
     return (min_spacing, maj_spacing)
 
 
-def period_break(dates, period):
+def period_break(dates: PeriodIndex, period: str) -> np.ndarray:
     """
     Returns the indices where the given period changes.
 
@@ -489,7 +489,7 @@ def period_break(dates, period):
     return np.nonzero(current - previous)[0]
 
 
-def has_level_label(label_flags, vmin):
+def has_level_label(label_flags: np.ndarray, vmin: float) -> bool:
     """
     Returns true if the ``label_flags`` indicate there is at least one label
     for this level.
@@ -984,18 +984,24 @@ class TimeSeries_DateFormatter(Formatter):
     ----------
     freq : {int, string}
         Valid frequency specifier.
-    minor_locator : {False, True}
+    minor_locator : bool, default False
         Whether the current formatter should apply to minor ticks (True) or
         major ticks (False).
-    dynamic_mode : {True, False}
+    dynamic_mode : bool, default True
         Whether the formatter works in dynamic mode or not.
     """
 
-    def __init__(self, freq, minor_locator=False, dynamic_mode=True, plot_obj=None):
+    def __init__(
+        self,
+        freq,
+        minor_locator: bool = False,
+        dynamic_mode: bool = True,
+        plot_obj=None,
+    ):
         freq = to_offset(freq)
         self.format = None
         self.freq = freq
-        self.locs = []
+        self.locs: List[Any] = []  # unused, for matplotlib compat
         self.formatdict = None
         self.isminor = minor_locator
         self.isdynamic = dynamic_mode