| Official Name: | Willow Lake, Illinois |
| Settlement Type: | Census-designated place |
| Pushpin Map: | Illinois#USA |
| Pushpin Label: | Willow Lake |
| Coordinates: | 42.3331°N -89.635°W |
| Subdivision Type: | Country |
| Subdivision Type1: | State |
| Subdivision Name1: | Illinois |
| Subdivision Type2: | County |
| Subdivision Name2: | Stephenson |
| Subdivision Type3: | Townships |
| Subdivision Name3: | Harlem Lancaster |
| Area Footnotes: | [1] |
| Area Total Sq Mi: | 2.77 |
| Area Land Sq Mi: | 2.73 |
| Area Water Sq Mi: | 0.04 |
| Area Total Km2: | 7.17 |
| Area Land Km2: | 7.08 |
| Area Water Km2: | 0.10 |
| Population As Of: | 2020 |
| Population Density Km2: | 145.01 |
| Timezone: | Central (CST) |
| Utc Offset: | -6 |
| Timezone Dst: | CDT |
| Utc Offset Dst: | -5 |
| Elevation Ft: | 820 |
| Postal Code Type: | ZIP Code |
| Postal Code: | 61032 (Freeport) |
| Area Code: | 815, 779 |
| Blank Name: | FIPS code |
| Blank Info: | 17-82029 |
| Blank1 Name: | GNIS feature ID |
| Blank1 Info: | 2806586 |
| Population Total: | 1026 |
| Unit Pref: | Imperial |
| Population Density Sq Mi: | 375.55 |
Willow Lake is a census-designated place (CDP) surrounding a lake of the same name in Stephenson County, Illinois, United States. It is in the center of the county, on the north side of U.S. Route 20 and 3miles north of the center of Freeport, the county seat.
Willow Lake was first listed as a CDP prior to the 2020 census.