First three digits · Illinois
ZIP Codes Starting with
6 ZIP codes start with 603, sorted at the Carol Stream, IL (SCF 601) sectional center (USPS labeling list L005, effective October 1, 2026) in Illinois: 4 residential ZIP codes across 2 counties and 2 PO Box or single-organization codes (Census 2020 ZCTAs and GeoNames postal codes, October 2026).
What do the digits 603 mean?
The first digit, 6, is one of ten national areas (Illinois, Kansas, Missouri and Nebraska). The first three, 603, route mail to a sectional center: USPS labeling list L005 (effective October 1, 2026) sends letters for 603 to the Carol Stream, IL (SCF 601) facility. The last two digits pick the delivery area. By residents, the largest town names among the 603 ZIP codes are Oak Park and River Forest.
The same facility sorts 2 prefixes, 95 ZIP codes in all: 601, 603.
Where are the 603 ZIP codes?
Source: U.S. Census Bureau, 2020 ZCTA cartographic boundaries; ACS 2020-2024 5-year estimates (B19013).
All ZIP codes starting with 603
| County | ||||||
|---|---|---|---|---|---|---|
| 60301 | Oak Park | Cook County | 3,475 | 17,821 | $99k | $247k |
| 60302 | Oak Park | Cook County | 32,862 | 11,121 | $101k | $474k |
| 60303 | Oak Park | Cook County | PO Box or unique | – | – | – |
| 60304 | Oak Park | Cook County | 16,955 | 10,939 | $136k | $467k |
| 60305 | River Forest | Cook County | 11,992 | 4,841 | $147k | $687k |
| 60399 | Wood Dale | DuPage County | PO Box or unique | – | – | – |
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates; GeoNames postal codes (CC BY 4.0) for codes without a residential area.