ZIP codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group (or perhaps a large city) and the fourth and fifth digits representing more specific areas, such as small towns or regions of that city. The main town in a region (if applicable) often gets the first ZIP codes for that region; afterward, the numerical order often follows the alphabetical order. 

Connecticut zip codes all start with "0" as well as Massachusetts, Maine, New Hampshire, New Jersey, Rhode Island, Vermont , Virgin Islands and Puerto Rico.