counter for houses, households, apartments
Used to count residential units. Often seen in addresses, real estate, and demographic contexts.
この町には約二千戸の家がある。
There are about two thousand houses in this town.
マンションの一戸を借りた。
I rented one apartment in the building.
This apartment building has 50 units.
About 100 houses are built in this area.
戸 counts residential units or households (often in statistics), while 軒 is the everyday counter for buildings, especially individual houses and shops.
The kanji 戸 originally means 'door' and came to represent a household or dwelling. The reading こ is the native Japanese kun'yomi.