ZIP Code 40121 — Fort Knox, KY
40121 is a standard (street delivery) ZIP code serving Fort Knox, Kentucky, in Hardin County. To mail something here you only need these five digits — but the four-digit extension narrows delivery to a single point, and it is what USPS bulk postage discounts are priced on.
ZIP code 40121 at a glance
| ZIP code | 40121 |
|---|---|
| Primary city | Fort Knox |
| State | Kentucky (KY) |
| County | Hardin FIPS 21093 |
| ZIP type | Standard (street delivery) |
| Time zone | America/New_York |
| Population | 8,836 |
| Coordinates | 37.926140, -85.952920 |
How ZIP+4 works in 40121
The four digits after the hyphen encode a delivery segment inside 40121. In practice one segment usually means:
- One side of one block — odd numbers on a street between two cross streets
- A single large building, or one floor of it
- A group of PO boxes, sometimes a single box
- A single business that receives enough mail to warrant its own code
That is why 40121 has no single ZIP+4: two neighbors across the street from each other usually have different ones. Enter a street address above and we will return the exact nine-digit code along with the standardized USPS address format.
Nearby ZIP codes
Showing the closest twelve. See every ZIP code within 25 miles of 40121.
| ZIP | City | Distance |
|---|---|---|
| 40155 | Muldraugh, KY | 2.6 mi |
| 40177 | West Point, KY | 5.4 mi |
| 40160 | Radcliff, KY | 7.7 mi |
| 40117 | Ekron, KY | 9.5 mi |
| 47135 | Laconia, IN | 10.3 mi |
| 40175 | Vine Grove, KY | 10.4 mi |
| 40108 | Brandenburg, KY | 12.1 mi |
| 40272 | Louisville, KY | 12.1 mi |
| 47117 | Elizabeth, IN | 12.4 mi |
| 40162 | Rineyville, KY | 13 mi |
| 40109 | Brooks, KY | 14.1 mi |
| 40142 | Guston, KY | 14.3 mi |
Questions about 40121
What is the ZIP+4 code for 40121?
40121 is the five-digit ZIP code. The ZIP+4 adds four more digits that identify a specific delivery point — usually one side of a city block, a single building, or a group of PO boxes. Because those four digits change from address to address within 40121, you need to look up a specific street address to get them.
What city is 40121?
40121 is assigned to Fort Knox, Kentucky, in Hardin County.
Do I need to use the ZIP+4?
It is optional for ordinary mail, but it speeds up sorting and it is required for most USPS bulk-mail postage discounts. Many address-verification and e-commerce systems also use ZIP+4 to confirm a delivery point exists.
Need thousands of these?
Upload a CSV and get ZIP+4, county, carrier route, and delivery-point data appended to every row — or call the API directly.