| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| J D Carney Mobile Home Park | city | Illinois | United States | 37.76 | -89.08 | 830 | |
| J and J Mobile Home Park | city | Illinois | United States | 42.35 | -90.00 | 1046 | |
| Jackson | city | Illinois | United States | 38.72 | -87.65 | 830 | |
| Jackson Park Highlands | city | Illinois | United States | 41.77 | -87.58 | 830 | |
| Jackson Park Terrace | city | Illinois | United States | 41.78 | -87.59 | 830 | |
| Jacksonville | city | Illinois | United States | 39.73 | -90.23 | 830 | |
| Jacob | city | Illinois | United States | 37.75 | -89.54 | 357 | |
| Jalapa | city | Illinois | United States | 39.22 | -90.32 | 830 | |
| Jamaica | city | Illinois | United States | 39.99 | -87.81 | 830 | |
| Jamesburg | city | Illinois | United States | 40.26 | -87.75 | 830 | |
| Jamestown | city | Illinois | United States | 38.05 | -89.53 | 830 | |
| Jamestown | city | Illinois | United States | 38.73 | -89.51 | 830 | |
| Jamestown (historical) | city | Illinois | United States | 38.04 | -88.37 | 830 | |
| Jane Addams Homes | city | Illinois | United States | 41.87 | -87.66 | 830 | |
| Janesville | city | Illinois | United States | 39.37 | -88.24 | 830 | |
| Jaques | city | Illinois | United States | 39.88 | -90.74 | 830 | |
| Jefferson City | city | Illinois | United States | 38.38 | -89.04 | 830 | |
| Jefferson City (historical) | city | Illinois | United States | 38.15 | -88.46 | 830 | |
| Jefferson Corners | city | Illinois | United States | 41.61 | -89.98 | 830 | |
| Jefferson Park | city | Illinois | United States | 41.97 | -87.76 | 830 | |
| Jeffery Manor | city | Illinois | United States | 41.72 | -87.57 | 830 | |
| Jeiseyville | city | Illinois | United States | 39.58 | -89.41 | 830 | |
| Jeisyville | city | Illinois | United States | 39.58 | -89.41 | 830 | |
| Jenkins | city | Illinois | United States | 40.15 | -89.03 | 830 | |
| Jenkins | city | Illinois | United States | 37.85 | -88.93 | 830 | |
| Jerome | city | Illinois | United States | 39.77 | -89.68 | 830 | |
| Jerseyville | city | Illinois | United States | 39.12 | -90.33 | 830 | |
| Jess | city | Illinois | United States | 39.76 | -89.67 | 830 | |
| Jessical Lane Subdivision | city | Illinois | United States | 42.12 | -87.86 | 830 | |
| Jewell Road | city | Illinois | United States | 41.88 | -88.14 | 830 | |
| Jewett | city | Illinois | United States | 39.21 | -88.25 | 830 | |
| Jim Davis Mobile Home Park | city | Illinois | United States | 38.09 | -88.18 | 400 | |
| Jimtown | city | Illinois | United States | 39.90 | -88.36 | 830 | |
| Jimtown | city | Illinois | United States | 38.99 | -89.21 | 830 | |
| Joetta | city | Illinois | United States | 40.43 | -90.93 | 830 | |
| Johannisburg | city | Illinois | United States | 38.38 | -89.65 | 830 | |
| Johnsburg | city | Illinois | United States | 42.38 | -88.24 | 830 | |
| Johnsonville | city | Illinois | United States | 38.52 | -88.54 | 830 | |
| Johnsonville | city | Illinois | United States | 40.21 | -87.67 | 830 | |
| Johnston City | city | Illinois | United States | 37.82 | -88.93 | 413 | |
| Johnstown | city | Illinois | United States | 39.36 | -88.29 | 830 | |
| Joliet | city | Illinois | United States | 41.53 | -88.08 | 830 | |
| Jones | city | Illinois | United States | 39.45 | -88.34 | 830 | |
| Jones Ridge | city | Illinois | United States | 37.80 | -89.63 | 357 | |
| Jonesboro | city | Illinois | United States | 37.45 | -89.27 | 830 | |
| Jonesville | city | Illinois | United States | 41.31 | -89.07 | 830 | |
| Jonesville | city | Illinois | United States | 42.33 | -89.08 | 830 | |
| Joppa | city | Illinois | United States | 37.21 | -88.84 | 331 | |
| Joppa Junction | city | Illinois | United States | 37.33 | -89.03 | 383 | |
| Jordanville (historical) | city | Illinois | United States | 39.86 | -90.10 | 830 | |
| Joslin | city | Illinois | United States | 41.56 | -90.22 | 830 | |
| Joy | city | Illinois | United States | 41.20 | -90.88 | 830 | |
| Joy Prairie | city | Illinois | United States | 39.79 | -90.30 | 830 | |
| Juanitas Mobile Home Park | city | Illinois | United States | 37.74 | -88.94 | 830 | |
| Judson (historical) | city | Illinois | United States | 41.25 | -87.64 | 830 | |
| Jules | city | Illinois | United States | 39.97 | -90.26 | 830 | |
| Julien Hill | city | Illinois | United States | 37.48 | -88.48 | 830 | |
| Junction | city | Illinois | United States | 37.72 | -88.24 | 380 | |
| Junction City | city | Illinois | United States | 38.58 | -89.13 | 830 | |
| Justice | city | Illinois | United States | 41.74 | -87.84 | 830 |