deserialize json string for multiple results

Please try this:

public class postalCodes        {            public string adminName2 { get; set; }            public int adminCode2 { get; set; }            public string adminCode1 { get; set; }            public int postalCode { get; set; }            public string countryCode { get; set; }            public double lng { get; set; }            public string placeName { get; set; }            public double lat { get; set; }            public string adminName1 { get; set; }        }        public class DataContainer        {            public List<postalCodes> postalCodes { get; set; }        }        [Test]        public void TestJson()        {            string input = "{\"postalCodes\":[{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10001\",\"countryCode\":\"US\",\"lng\":-73.996705,\"placeName\":\"New York City\",\"lat\":40.74838,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10019\",\"countryCode\":\"US\",\"lng\":-73.985834,\"placeName\":\"New York City\",\"lat\":40.765069,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10021\",\"countryCode\":\"US\",\"lng\":-73.958805,\"placeName\":\"New York City\",\"lat\":40.768476,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10022\",\"countryCode\":\"US\",\"lng\":-73.965703,\"placeName\":\"New York City\",\"lat\":40.757091,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10036\",\"countryCode\":\"US\",\"lng\":-73.991826,\"placeName\":\"New York City\",\"lat\":40.759724,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10065\",\"countryCode\":\"US\",\"lng\":-73.96379,\"placeName\":\"New York City\",\"lat\":40.76507,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10003\",\"countryCode\":\"US\",\"lng\":-73.989223,\"placeName\":\"New York City\",\"lat\":40.731253,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10010\",\"countryCode\":\"US\",\"lng\":-73.981328,\"placeName\":\"New York City\",\"lat\":40.737476,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10011\",\"countryCode\":\"US\",\"lng\":-73.99963,\"placeName\":\"New York City\",\"lat\":40.740225,\"adminName1\":\"New York\"},{\"adminName2\":\"New York\",\"adminCode2\":\"061\",\"adminCode1\":\"NY\",\"postalCode\":\"10012\",\"countryCode\":\"US\",\"lng\":-73.998284,\"placeName\":\"New York City\",\"lat\":40.72553,\"adminName1\":\"New York\"}]}";            var observation = JsonConvert.DeserializeObject<DataContainer>(input);         }

Looks like you have an array and this maps to a List<postalCodes> instead of postalCodes.

var observation = JsonConvert.DeserializeObject<List<postalCodes>>(jsonResponse);