Chickens may be kept as long as they do not create a nuisance that is detrimental to public health, such as odor or other unsanitary conditions.

Chicken care essentials 

Once hens have been adopted, proper care and housing are vital. In addition to regular daily attention, feed and clean water, and securing them in their shelter at night, the following care principles are also essential.
 

• Chickens are heat- and cold-sensitive
  

  Like dogs and cats, chickens must have shelter to protect them from temperature extremes. Hens and roosters with large single combs are prone to frostbite in cooler climates, and all chickens need shade during periods of heat. It is important that the shelter is both insulated and well-ventilated. Straw bedding will add comfort and warmth to a shelter's floor space, but it should be replaced regularly with new, clean straw.

• Predator protection is vital

  Chickens need absolutely secure shelter at night or they can easily fall prey to urban wildlife like raccoons and opossums. Dogs may also attack chickens. They must be completely enclosed in a safe henhouse, with four solid walls and a sturdy roof, every night. Predators can also dig under fences and walls, so this should be considered when planning the chickens' home. During the day, chickens should be kept in a fully-fenced enclosure or yard with proper protection from aerial day-time predators, neighborhood dogs and, in the case of small bantam hens, free-roaming cats.
   

• Hens need an appropriate environment

  Hens need an enclosed nesting space (a "nestbox") in which to lay their eggs. They also need an elevated roost on which to perch at night; this is where they prefer to sleep. Hens enjoy loose substrate such as dirt, sand, or peat for dustbathing, and they should also have free access to grass and other vegetation to engage in natural pecking, scratching, and foraging behaviors. Often-used areas may become denuded, and it is important to provide plenty of space, giving them as much room as possible to express natural behavior outdoors. Hen houses, coops, and runs must be kept very clean at all times, for the health of the chickens and the food safety of the eggs.
   

• Chickens will require veterinary care

  While it may be tempting to think of a backyard flock as a source of inexpensive eggs, hens, like cats and dogs, require periodic veterinary care. Chickens can become ill or get injured, and vet exams and treatment can easily cost over $100 per visit. These expenses should be carefully considered before the decision is made to keep backyard chickens. Not all avian veterinarians are experienced with chickens, so be sure to locate a trusted poultry vet in your area ahead of time.
   

• Vacation help is a must

  Since chickens require daily care, a designated caretaker must be arranged for vacations and other periods away from the house. Someone must be present to feed and water the hens and to put them inside their secure shelter every evening.
   

• Chicken nutrition is important

  It is a common misperception that chickens can be fed on corn kernels or kitchen scraps alone. Chickens need a balanced diet, like one of the commercially available feeds that have been carefully formulated by nutritionists specifically for adult hens. The protein requirements of chickens change with the birds' age, so it's important to feed an age-appropriate diet. 
  
  Laying hens also need access to a supplemental source of course calcium, such as limestone (available at livestock supply stores) if their feed ration does not already contain enough. In addition to calcium, hard insoluble granite grit should be fed, free choice, 2 or 3 days per month. 
  
  Chickens enjoy fresh fruits, grains, and vegetables in addition to their regular feed, but certain plants can be toxic. Avoid raw green potato peels, dried or undercooked beans, and avocados. Chickens should receive fresh feed and water daily—discard any feed that is old, moldy, or stale.   
  
  The Alabama Cooperative Extension System has published a detailed page on the feeding requirements of backyard chicken flocks throughout their lives.
   
  

• Prevent disease

  Chickens can carry and become ill from a variety of infectious diseases. It is important to keep the hens' environment clean with regular manure removal, and by washing the feed and water containers. You should also avoid mixing birds from different flocks. (Temporarily quarantine any new birds for two weeks and watch them closely for signs of illness or parasites before introducing them into an already established group.) Don't share equipment with neighbors (each chicken house should have dedicated tools, wheelbarrows, buckets, etc.), because pathogenic organisms can travel on these items. Diseases can spread to chickens from pet birds and wild birds, so limit contact where possible.
   

• Give your birds plenty of attention

  If you spend time watching and interacting with your chickens, you will find that each one has a unique personality, and they are friendly and curious when treated kindly. They display interesting behavior patterns such as dustbathing and foraging, and their complex social interactions are entertaining to observe. Enjoy their antics, and remember that your hens are completely dependent on you for responsible, committed care for their entire lives.

Source:
Humane Society of the United States