Function to return the two letter state abbreviation from a US zip code.

state-from-zipcode.js

function stateFromZIPCode (zipcode) {

    var i, item, l, state, statesByZIP;

    // list of zip code ranges and the states they reside in
    statesByZIP = [
        [ 210, 3897, "NH" ],
        [ 501, 544, "NY" ],
        [ 1001, 5544, "MA" ],
        [ 2801, 2940, "RI" ],
        [ 3901, 4992, "ME" ],
        [ 5001, 5907, "VT" ],
        [ 6001, 6928, "CT" ],
        [ 6390, 6390, "NY" ],
        [ 7001, 8989, "NJ" ],
        [ 10001, 14925, "NY" ],
        [ 15001, 19640, "PA" ],
        [ 19701, 19980, "DE" ],
        [ 20101, 20199, "VA" ],
        [ 20601, 21930, "MD" ],
        [ 22002, 24658, "VA" ],
        [ 24701, 26886, "WV" ],
        [ 27006, 28909, "NC" ],
        [ 29001, 29945, "SC" ],
        [ 30002, 31999, "GA" ],
        [ 32004, 34997, "FL" ],
        [ 35004, 36925, "AL" ],
        [ 37010, 38589, "TN" ],
        [ 38601, 39776, "MS" ],
        [ 39901, 39901, "GA" ],
        [ 40003, 42788, "KY" ],
        [ 43001, 45999, "OH" ],
        [ 46001, 47997, "IN" ],
        [ 48001, 49971, "MI" ],
        [ 50001, 52809, "IA" ],
        [ 53001, 54990, "WI" ],
        [ 55001, 56763, "MN" ],
        [ 57001, 57799, "SD" ],
        [ 58001, 58856, "ND" ],
        [ 59001, 59937, "MT" ],
        [ 60001, 62999, "IL" ],
        [ 63001, 65899, "MO" ],
        [ 66002, 67954, "KS" ],
        [ 68001, 69367, "NE" ],
        [ 70001, 71497, "LA" ],
        [ 71601, 72959, "AR" ],
        [ 73001, 73199, "OK" ],
        [ 73301, 73344, "TX" ],
        [ 73401, 74966, "OK" ],
        [ 75001, 79999, "TX" ],
        [ 80001, 81658, "CO" ],
        [ 82001, 83128, "WY" ],
        [ 83201, 83888, "ID" ],
        [ 84001, 84791, "UT" ],
        [ 85001, 86556, "AZ" ],
        [ 87001, 88441, "NM" ],
        [ 88510, 88595, "TX" ],
        [ 88901, 89883, "NV" ],
        [ 90001, 96162, "CA" ],
        [ 96701, 96898, "HI" ],
        [ 97001, 97920, "OR" ],
        [ 98001, 99403, "WA" ],
        [ 99501, 99950, "AK" ]
    ];

    // ignore if zipcode is a string and is less than five characters
    if (zipcode.length && zipcode.length < 5) {
        return;
    }

    // only take the first five characters
    if (zipcode.slice) {
        zipcode = zipcode.slice(0, 6);
    }

    // convert from string to integer
    zipcode = parseInt(zipcode, 10);
    if (!isNaN(zipcode)) {

        // zipcode is a number
        // find the state which contains this zipcode
        // use a for loop so we can break out
        l = statesByZIP.length;
        for (i = 0; i < l; i += 1) {

            item = statesByZIP[i];
            if (zipcode >= item[0] && zipcode <= item[1]) {
                state = item[2];
                break;
            }

        }


    }

    return state;

}