diff --git a/homeassistant/components/mill/__init__.py b/homeassistant/components/mill/__init__.py
index 11199e126cf..dd0c4035dd7 100644
--- a/homeassistant/components/mill/__init__.py
+++ b/homeassistant/components/mill/__init__.py
@@ -11,6 +11,7 @@ from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import CONF_IP_ADDRESS, CONF_PASSWORD, CONF_USERNAME, Platform
 from homeassistant.core import HomeAssistant
 from homeassistant.exceptions import ConfigEntryNotReady
+from homeassistant.helpers import device_registry as dr
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 
 from .const import CLOUD, CONNECTION_TYPE, DOMAIN, LOCAL
@@ -55,6 +56,18 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
     await data_coordinator.async_config_entry_first_refresh()
     hass.data[DOMAIN][conn_type][key] = data_coordinator
 
+    if entry.data.get(CONNECTION_TYPE) == CLOUD:
+        device_registry = dr.async_get(hass)
+        for mill_device in mill_data_connection.devices.values():
+            # migrate to new device ids
+            device_entry = device_registry.async_get_device(
+                identifiers={(DOMAIN, mill_device.device_id)}
+            )
+            if device_entry and entry.entry_id in device_entry.config_entries:
+                device_registry.async_update_device(
+                    device_entry.id, new_identifiers={(DOMAIN, mill_device.mac_address)}
+                )
+
     await hass.config_entries.async_forward_entry_setups(entry, PLATFORMS)
     return True
 
diff --git a/homeassistant/components/mill/climate.py b/homeassistant/components/mill/climate.py
index 4f700d24e1b..a4f0ef04755 100644
--- a/homeassistant/components/mill/climate.py
+++ b/homeassistant/components/mill/climate.py
@@ -113,7 +113,7 @@ class MillHeater(CoordinatorEntity[MillDataUpdateCoordinator], ClimateEntity):
         self._id = heater.device_id
         self._attr_unique_id = heater.device_id
         self._attr_device_info = DeviceInfo(
-            identifiers={(DOMAIN, heater.device_id)},
+            identifiers={(DOMAIN, heater.mac_address)},
             manufacturer=MANUFACTURER,
             model=heater.model,
             name=heater.name,
@@ -197,16 +197,16 @@ class LocalMillHeater(CoordinatorEntity[MillDataUpdateCoordinator], ClimateEntit
     def __init__(self, coordinator: MillDataUpdateCoordinator) -> None:
         """Initialize the thermostat."""
         super().__init__(coordinator)
-        if mac := coordinator.mill_data_connection.mac_address:
-            self._attr_unique_id = mac
-            self._attr_device_info = DeviceInfo(
-                connections={(CONNECTION_NETWORK_MAC, mac)},
-                configuration_url=self.coordinator.mill_data_connection.url,
-                manufacturer=MANUFACTURER,
-                model="Generation 3",
-                name=coordinator.mill_data_connection.name,
-                sw_version=coordinator.mill_data_connection.version,
-            )
+        mac = coordinator.mill_data_connection.mac_address
+        self._attr_unique_id = mac
+        self._attr_device_info = DeviceInfo(
+            connections={(CONNECTION_NETWORK_MAC, mac)},
+            configuration_url=self.coordinator.mill_data_connection.url,
+            manufacturer=MANUFACTURER,
+            model="Generation 3",
+            name=coordinator.mill_data_connection.name,
+            sw_version=coordinator.mill_data_connection.version,
+        )
 
         self._update_attr()
 
diff --git a/homeassistant/components/mill/sensor.py b/homeassistant/components/mill/sensor.py
index c4b975ab039..2ef14204f2e 100644
--- a/homeassistant/components/mill/sensor.py
+++ b/homeassistant/components/mill/sensor.py
@@ -193,7 +193,7 @@ class MillSensor(CoordinatorEntity, SensorEntity):
         self._available = False
         self._attr_unique_id = f"{mill_device.device_id}_{entity_description.key}"
         self._attr_device_info = DeviceInfo(
-            identifiers={(DOMAIN, mill_device.device_id)},
+            identifiers={(DOMAIN, mill_device.mac_address)},
             name=mill_device.name,
             manufacturer=MANUFACTURER,
             model=mill_device.model,
@@ -227,16 +227,17 @@ class LocalMillSensor(CoordinatorEntity, SensorEntity):
         super().__init__(coordinator)
 
         self.entity_description = entity_description
-        if mac := coordinator.mill_data_connection.mac_address:
-            self._attr_unique_id = f"{mac}_{entity_description.key}"
-            self._attr_device_info = DeviceInfo(
-                connections={(CONNECTION_NETWORK_MAC, mac)},
-                configuration_url=self.coordinator.mill_data_connection.url,
-                manufacturer=MANUFACTURER,
-                model="Generation 3",
-                name=coordinator.mill_data_connection.name,
-                sw_version=coordinator.mill_data_connection.version,
-            )
+        mac = coordinator.mill_data_connection.mac_address
+        self._attr_unique_id = f"{mac}_{entity_description.key}"
+        self._attr_device_info = DeviceInfo(
+            connections={(CONNECTION_NETWORK_MAC, mac)},
+            configuration_url=self.coordinator.mill_data_connection.url,
+            identifiers={(DOMAIN, mac)},
+            manufacturer=MANUFACTURER,
+            model="Generation 3",
+            name=coordinator.mill_data_connection.name,
+            sw_version=coordinator.mill_data_connection.version,
+        )
 
     @property
     def native_value(self):