A PO BOX number can be less than or more than four digit. For post office boxes, the general rule is that each box has its own ZIP+4 code.
The last four digit is often one of the following:
1. Zero plus the last three digits of the box number (eg. PO BOX 1001, Los Angeles CA 90001-0001).
2. The last four digits of the box number (eg. PO BOX 9991, Twin Peaks CA 92391-9991).
3. If the box number is less than four digits, enough zeros prepended to the front of the box number to produce a four-digit number(eg. PO BOX 1, Shreveport LA 71161-0001).
However, there is no uniform rule, the zip code plus four is for reference only, the ZIP+4 code must be looked up individually for each box in the USPS offical website.
PO BOX 21, GRUNDY CENTER, IA 50638-0021
PO BOX 22, GRUNDY CENTER, IA 50638-0022
PO BOX 23, GRUNDY CENTER, IA 50638-0023
PO BOX 24, GRUNDY CENTER, IA 50638-0024
PO BOX 25, GRUNDY CENTER, IA 50638-0025
PO BOX 26, GRUNDY CENTER, IA 50638-0026
PO BOX 27, GRUNDY CENTER, IA 50638-0027
PO BOX 28, GRUNDY CENTER, IA 50638-0028
PO BOX 29, GRUNDY CENTER, IA 50638-0029
PO BOX 30, GRUNDY CENTER, IA 50638-0030
PO BOX 31, GRUNDY CENTER, IA 50638-0031
PO BOX 32, GRUNDY CENTER, IA 50638-0032
PO BOX 33, GRUNDY CENTER, IA 50638-0033
PO BOX 34, GRUNDY CENTER, IA 50638-0034
PO BOX 35, GRUNDY CENTER, IA 50638-0035
PO BOX 36, GRUNDY CENTER, IA 50638-0036
PO BOX 37, GRUNDY CENTER, IA 50638-0037
PO BOX 38, GRUNDY CENTER, IA 50638-0038
PO BOX 39, GRUNDY CENTER, IA 50638-0039
PO BOX 40, GRUNDY CENTER, IA 50638-0040
PO BOX 41, GRUNDY CENTER, IA 50638-0041
PO BOX 42, GRUNDY CENTER, IA 50638-0042
PO BOX 43, GRUNDY CENTER, IA 50638-0043
PO BOX 44, GRUNDY CENTER, IA 50638-0044
PO BOX 45, GRUNDY CENTER, IA 50638-0045
PO BOX 46, GRUNDY CENTER, IA 50638-0046
PO BOX 47, GRUNDY CENTER, IA 50638-0047
PO BOX 48, GRUNDY CENTER, IA 50638-0048
PO BOX 49, GRUNDY CENTER, IA 50638-0049
PO BOX 50, GRUNDY CENTER, IA 50638-0050
PO BOX 51, GRUNDY CENTER, IA 50638-0051
PO BOX 52, GRUNDY CENTER, IA 50638-0052
PO BOX 53, GRUNDY CENTER, IA 50638-0053
PO BOX 54, GRUNDY CENTER, IA 50638-0054
PO BOX 55, GRUNDY CENTER, IA 50638-0055
PO BOX 56, GRUNDY CENTER, IA 50638-0056
PO BOX 57, GRUNDY CENTER, IA 50638-0057
PO BOX 58, GRUNDY CENTER, IA 50638-0058
PO BOX 59, GRUNDY CENTER, IA 50638-0059
PO BOX 60, GRUNDY CENTER, IA 50638-0060
PO BOX 61, GRUNDY CENTER, IA 50638-0061
PO BOX 62, GRUNDY CENTER, IA 50638-0062
PO BOX 63, GRUNDY CENTER, IA 50638-0063
PO BOX 64, GRUNDY CENTER, IA 50638-0064
PO BOX 65, GRUNDY CENTER, IA 50638-0065
PO BOX 66, GRUNDY CENTER, IA 50638-0066
PO BOX 67, GRUNDY CENTER, IA 50638-0067
PO BOX 68, GRUNDY CENTER, IA 50638-0068
PO BOX 69, GRUNDY CENTER, IA 50638-0069
PO BOX 70, GRUNDY CENTER, IA 50638-0070
PO BOX 71, GRUNDY CENTER, IA 50638-0071
PO BOX 72, GRUNDY CENTER, IA 50638-0072
PO BOX 73, GRUNDY CENTER, IA 50638-0073
PO BOX 74, GRUNDY CENTER, IA 50638-0074
PO BOX 75, GRUNDY CENTER, IA 50638-0075
PO BOX 76, GRUNDY CENTER, IA 50638-0076
PO BOX 77, GRUNDY CENTER, IA 50638-0077
PO BOX 78, GRUNDY CENTER, IA 50638-0078
PO BOX 79, GRUNDY CENTER, IA 50638-0079
PO BOX 80, GRUNDY CENTER, IA 50638-0080
PO BOX 81, GRUNDY CENTER, IA 50638-0081
PO BOX 82, GRUNDY CENTER, IA 50638-0082
PO BOX 83, GRUNDY CENTER, IA 50638-0083
PO BOX 84, GRUNDY CENTER, IA 50638-0084
PO BOX 85, GRUNDY CENTER, IA 50638-0085
PO BOX 86, GRUNDY CENTER, IA 50638-0086
PO BOX 87, GRUNDY CENTER, IA 50638-0087
PO BOX 88, GRUNDY CENTER, IA 50638-0088
PO BOX 89, GRUNDY CENTER, IA 50638-0089
PO BOX 90, GRUNDY CENTER, IA 50638-0090
PO BOX 91, GRUNDY CENTER, IA 50638-0091
PO BOX 92, GRUNDY CENTER, IA 50638-0092
PO BOX 93, GRUNDY CENTER, IA 50638-0093
PO BOX 94, GRUNDY CENTER, IA 50638-0094
PO BOX 95, GRUNDY CENTER, IA 50638-0095
PO BOX 96, GRUNDY CENTER, IA 50638-0096
PO BOX 97, GRUNDY CENTER, IA 50638-0097
PO BOX 98, GRUNDY CENTER, IA 50638-0098
PO BOX 99, GRUNDY CENTER, IA 50638-0099
PO BOX 100, GRUNDY CENTER, IA 50638-0100
PO BOX 101, GRUNDY CENTER, IA 50638-0101
PO BOX 102, GRUNDY CENTER, IA 50638-0102
PO BOX 103, GRUNDY CENTER, IA 50638-0103
PO BOX 104, GRUNDY CENTER, IA 50638-0104
PO BOX 105, GRUNDY CENTER, IA 50638-0105
PO BOX 106, GRUNDY CENTER, IA 50638-0106
PO BOX 107, GRUNDY CENTER, IA 50638-0107
PO BOX 108, GRUNDY CENTER, IA 50638-0108
PO BOX 109, GRUNDY CENTER, IA 50638-0109
PO BOX 110, GRUNDY CENTER, IA 50638-0110
PO BOX 111, GRUNDY CENTER, IA 50638-0111
PO BOX 112, GRUNDY CENTER, IA 50638-0112
PO BOX 113, GRUNDY CENTER, IA 50638-0113
PO BOX 114, GRUNDY CENTER, IA 50638-0114
PO BOX 115, GRUNDY CENTER, IA 50638-0115
PO BOX 116, GRUNDY CENTER, IA 50638-0116
PO BOX 117, GRUNDY CENTER, IA 50638-0117
PO BOX 118, GRUNDY CENTER, IA 50638-0118
PO BOX 119, GRUNDY CENTER, IA 50638-0119
PO BOX 120, GRUNDY CENTER, IA 50638-0120
PO BOX 121, GRUNDY CENTER, IA 50638-0121
PO BOX 122, GRUNDY CENTER, IA 50638-0122
PO BOX 123, GRUNDY CENTER, IA 50638-0123
PO BOX 124, GRUNDY CENTER, IA 50638-0124
PO BOX 125, GRUNDY CENTER, IA 50638-0125
PO BOX 126, GRUNDY CENTER, IA 50638-0126
PO BOX 127, GRUNDY CENTER, IA 50638-0127
PO BOX 128, GRUNDY CENTER, IA 50638-0128
PO BOX 129, GRUNDY CENTER, IA 50638-0129
PO BOX 130, GRUNDY CENTER, IA 50638-0130
PO BOX 131, GRUNDY CENTER, IA 50638-0131
PO BOX 132, GRUNDY CENTER, IA 50638-0132
PO BOX 133, GRUNDY CENTER, IA 50638-0133
PO BOX 134, GRUNDY CENTER, IA 50638-0134
PO BOX 135, GRUNDY CENTER, IA 50638-0135
PO BOX 136, GRUNDY CENTER, IA 50638-0136
PO BOX 137, GRUNDY CENTER, IA 50638-0137
PO BOX 138, GRUNDY CENTER, IA 50638-0138
PO BOX 139, GRUNDY CENTER, IA 50638-0139
PO BOX 140, GRUNDY CENTER, IA 50638-0140
PO BOX 141, GRUNDY CENTER, IA 50638-0141
PO BOX 142, GRUNDY CENTER, IA 50638-0142
PO BOX 143, GRUNDY CENTER, IA 50638-0143
PO BOX 144, GRUNDY CENTER, IA 50638-0144
PO BOX 145, GRUNDY CENTER, IA 50638-0145
PO BOX 146, GRUNDY CENTER, IA 50638-0146
PO BOX 147, GRUNDY CENTER, IA 50638-0147
PO BOX 148, GRUNDY CENTER, IA 50638-0148
PO BOX 149, GRUNDY CENTER, IA 50638-0149
PO BOX 150, GRUNDY CENTER, IA 50638-0150
PO BOX 151, GRUNDY CENTER, IA 50638-0151
PO BOX 152, GRUNDY CENTER, IA 50638-0152
PO BOX 153, GRUNDY CENTER, IA 50638-0153
PO BOX 154, GRUNDY CENTER, IA 50638-0154
PO BOX 155, GRUNDY CENTER, IA 50638-0155
PO BOX 156, GRUNDY CENTER, IA 50638-0156
PO BOX 157, GRUNDY CENTER, IA 50638-0157
PO BOX 158, GRUNDY CENTER, IA 50638-0158
PO BOX 159, GRUNDY CENTER, IA 50638-0159
PO BOX 160, GRUNDY CENTER, IA 50638-0160
PO BOX 161, GRUNDY CENTER, IA 50638-0161
PO BOX 162, GRUNDY CENTER, IA 50638-0162
PO BOX 163, GRUNDY CENTER, IA 50638-0163
PO BOX 164, GRUNDY CENTER, IA 50638-0164
PO BOX 165, GRUNDY CENTER, IA 50638-0165
PO BOX 166, GRUNDY CENTER, IA 50638-0166
PO BOX 167, GRUNDY CENTER, IA 50638-0167
PO BOX 168, GRUNDY CENTER, IA 50638-0168
PO BOX 169, GRUNDY CENTER, IA 50638-0169
PO BOX 170, GRUNDY CENTER, IA 50638-0170
PO BOX 171, GRUNDY CENTER, IA 50638-0171
PO BOX 172, GRUNDY CENTER, IA 50638-0172
PO BOX 173, GRUNDY CENTER, IA 50638-0173
PO BOX 174, GRUNDY CENTER, IA 50638-0174
PO BOX 175, GRUNDY CENTER, IA 50638-0175
PO BOX 176, GRUNDY CENTER, IA 50638-0176
PO BOX 177, GRUNDY CENTER, IA 50638-0177
PO BOX 178, GRUNDY CENTER, IA 50638-0178
PO BOX 179, GRUNDY CENTER, IA 50638-0179
PO BOX 180, GRUNDY CENTER, IA 50638-0180
PO BOX 181, GRUNDY CENTER, IA 50638-0181
PO BOX 182, GRUNDY CENTER, IA 50638-0182
PO BOX 183, GRUNDY CENTER, IA 50638-0183
PO BOX 184, GRUNDY CENTER, IA 50638-0184
PO BOX 185, GRUNDY CENTER, IA 50638-0185
PO BOX 186, GRUNDY CENTER, IA 50638-0186
PO BOX 187, GRUNDY CENTER, IA 50638-0187
PO BOX 188, GRUNDY CENTER, IA 50638-0188
PO BOX 189, GRUNDY CENTER, IA 50638-0189
PO BOX 190, GRUNDY CENTER, IA 50638-0190
PO BOX 191, GRUNDY CENTER, IA 50638-0191
PO BOX 192, GRUNDY CENTER, IA 50638-0192
PO BOX 193, GRUNDY CENTER, IA 50638-0193
PO BOX 194, GRUNDY CENTER, IA 50638-0194
PO BOX 195, GRUNDY CENTER, IA 50638-0195
PO BOX 196, GRUNDY CENTER, IA 50638-0196
PO BOX 197, GRUNDY CENTER, IA 50638-0197
PO BOX 198, GRUNDY CENTER, IA 50638-0198
PO BOX 199, GRUNDY CENTER, IA 50638-0199
PO BOX 200, GRUNDY CENTER, IA 50638-0200
PO BOX 201, GRUNDY CENTER, IA 50638-0201
PO BOX 202, GRUNDY CENTER, IA 50638-0202
PO BOX 203, GRUNDY CENTER, IA 50638-0203
PO BOX 204, GRUNDY CENTER, IA 50638-0204
PO BOX 205, GRUNDY CENTER, IA 50638-0205
PO BOX 206, GRUNDY CENTER, IA 50638-0206
PO BOX 207, GRUNDY CENTER, IA 50638-0207
PO BOX 208, GRUNDY CENTER, IA 50638-0208
PO BOX 209, GRUNDY CENTER, IA 50638-0209
PO BOX 210, GRUNDY CENTER, IA 50638-0210
PO BOX 211, GRUNDY CENTER, IA 50638-0211
PO BOX 212, GRUNDY CENTER, IA 50638-0212
PO BOX 213, GRUNDY CENTER, IA 50638-0213
PO BOX 214, GRUNDY CENTER, IA 50638-0214
PO BOX 215, GRUNDY CENTER, IA 50638-0215
PO BOX 216, GRUNDY CENTER, IA 50638-0216
PO BOX 217, GRUNDY CENTER, IA 50638-0217
PO BOX 218, GRUNDY CENTER, IA 50638-0218
PO BOX 219, GRUNDY CENTER, IA 50638-0219
PO BOX 220, GRUNDY CENTER, IA 50638-0220
PO BOX 221, GRUNDY CENTER, IA 50638-0221