diff --git a/.strict-typing b/.strict-typing
index ddf98accb9a..8373e0623f5 100644
--- a/.strict-typing
+++ b/.strict-typing
@@ -112,6 +112,7 @@ homeassistant.components.fastdotcom.*
 homeassistant.components.feedreader.*
 homeassistant.components.file_upload.*
 homeassistant.components.filesize.*
+homeassistant.components.filter.*
 homeassistant.components.fitbit.*
 homeassistant.components.flux_led.*
 homeassistant.components.forecast_solar.*
diff --git a/homeassistant/components/filter/sensor.py b/homeassistant/components/filter/sensor.py
index 700421e8876..e4166494ce4 100644
--- a/homeassistant/components/filter/sensor.py
+++ b/homeassistant/components/filter/sensor.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 
 from collections import Counter, deque
 from copy import copy
+from dataclasses import dataclass
 from datetime import datetime, timedelta
 from functools import partial
 import logging
@@ -40,7 +41,7 @@ import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity_platform import AddEntitiesCallback
 from homeassistant.helpers.event import async_track_state_change_event
 from homeassistant.helpers.reload import async_setup_reload_service
-from homeassistant.helpers.typing import ConfigType, DiscoveryInfoType
+from homeassistant.helpers.typing import ConfigType, DiscoveryInfoType, StateType
 from homeassistant.util.decorator import Registry
 import homeassistant.util.dt as dt_util
 
@@ -211,7 +212,7 @@ class SensorFilter(SensorEntity):
         self._attr_unique_id = unique_id
         self._entity = entity_id
         self._attr_native_unit_of_measurement = None
-        self._state: str | None = None
+        self._state: StateType = None
         self._filters = filters
         self._attr_icon = None
         self._attr_device_class = None
@@ -242,7 +243,7 @@ class SensorFilter(SensorEntity):
             self.async_write_ha_state()
             return
 
-        temp_state = new_state
+        temp_state = _State(new_state.last_updated, new_state.state)
 
         try:
             for filt in self._filters:
@@ -361,10 +362,10 @@ class SensorFilter(SensorEntity):
         )
 
     @property
-    def native_value(self) -> datetime | str | None:
+    def native_value(self) -> datetime | StateType:
         """Return the state of the sensor."""
         if self._state is not None and self.device_class == SensorDeviceClass.TIMESTAMP:
-            return datetime.fromisoformat(self._state)
+            return datetime.fromisoformat(str(self._state))
 
         return self._state
 
@@ -372,7 +373,9 @@ class SensorFilter(SensorEntity):
 class FilterState:
     """State abstraction for filter usage."""
 
-    def __init__(self, state):
+    state: str | float | int
+
+    def __init__(self, state: _State) -> None:
         """Initialize with HA State object."""
         self.timestamp = state.last_updated
         try:
@@ -380,7 +383,7 @@ class FilterState:
         except ValueError:
             self.state = state.state
 
-    def set_precision(self, precision):
+    def set_precision(self, precision: int) -> None:
         """Set precision of Number based states."""
         if isinstance(self.state, Number):
             value = round(float(self.state), precision)
@@ -395,6 +398,18 @@ class FilterState:
         return f"{self.timestamp} : {self.state}"
 
 
+@dataclass
+class _State:
+    """Simplified State class.
+
+    The standard State class only accepts string in `state`,
+    and we are only interested in two properties.
+    """
+
+    last_updated: datetime
+    state: str | float | int
+
+
 class Filter:
     """Filter skeleton."""
 
@@ -444,7 +459,7 @@ class Filter:
         """Implement filter."""
         raise NotImplementedError()
 
-    def filter_state(self, new_state: State) -> State:
+    def filter_state(self, new_state: _State) -> _State:
         """Implement a common interface for filters."""
         fstate = FilterState(new_state)
         if self._only_numbers and not isinstance(fstate.state, Number):
@@ -488,7 +503,10 @@ class RangeFilter(Filter, SensorEntity):
     def _filter_state(self, new_state: FilterState) -> FilterState:
         """Implement the range filter."""
 
-        if self._upper_bound is not None and new_state.state > self._upper_bound:
+        # We can cast safely here thanks to self._only_numbers = True
+        new_state_value = cast(float, new_state.state)
+
+        if self._upper_bound is not None and new_state_value > self._upper_bound:
 
             self._stats_internal["erasures_up"] += 1
 
@@ -500,7 +518,7 @@ class RangeFilter(Filter, SensorEntity):
             )
             new_state.state = self._upper_bound
 
-        elif self._lower_bound is not None and new_state.state < self._lower_bound:
+        elif self._lower_bound is not None and new_state_value < self._lower_bound:
 
             self._stats_internal["erasures_low"] += 1
 
@@ -537,10 +555,14 @@ class OutlierFilter(Filter, SensorEntity):
     def _filter_state(self, new_state: FilterState) -> FilterState:
         """Implement the outlier filter."""
 
-        median = statistics.median([s.state for s in self.states]) if self.states else 0
+        # We can cast safely here thanks to self._only_numbers = True
+        previous_state_values = [cast(float, s.state) for s in self.states]
+        new_state_value = cast(float, new_state.state)
+
+        median = statistics.median(previous_state_values) if self.states else 0
         if (
             len(self.states) == self.states.maxlen
-            and abs(new_state.state - median) > self._radius
+            and abs(new_state_value - median) > self._radius
         ):
 
             self._stats_internal["erasures"] += 1
@@ -574,9 +596,10 @@ class LowPassFilter(Filter, SensorEntity):
 
         new_weight = 1.0 / self._time_constant
         prev_weight = 1.0 - new_weight
-        new_state.state = (
-            prev_weight * self.states[-1].state + new_weight * new_state.state
-        )
+        # We can cast safely here thanks to self._only_numbers = True
+        prev_state_value = cast(float, self.states[-1].state)
+        new_state_value = cast(float, new_state.state)
+        new_state.state = prev_weight * prev_state_value + new_weight * new_state_value
 
         return new_state
 
@@ -622,7 +645,9 @@ class TimeSMAFilter(Filter, SensorEntity):
         start = new_state.timestamp - self._time_window
         prev_state = self.last_leak if self.last_leak is not None else self.queue[0]
         for state in self.queue:
-            moving_sum += (state.timestamp - start).total_seconds() * prev_state.state
+            # We can cast safely here thanks to self._only_numbers = True
+            prev_state_value = cast(float, prev_state.state)
+            moving_sum += (state.timestamp - start).total_seconds() * prev_state_value
             start = state.timestamp
             prev_state = state
 
diff --git a/mypy.ini b/mypy.ini
index cfb64b5348e..7da024bd3c1 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -874,6 +874,16 @@ disallow_untyped_defs = true
 warn_return_any = true
 warn_unreachable = true
 
+[mypy-homeassistant.components.filter.*]
+check_untyped_defs = true
+disallow_incomplete_defs = true
+disallow_subclassing_any = true
+disallow_untyped_calls = true
+disallow_untyped_decorators = true
+disallow_untyped_defs = true
+warn_return_any = true
+warn_unreachable = true
+
 [mypy-homeassistant.components.fitbit.*]
 check_untyped_defs = true
 disallow_incomplete_defs = true