| Official Name: | Township of Illinois |
| Settlement Type: | Township |
| Image Map1: | Map of Arkansas highlighting Washington County.svg |
| Mapsize1: | 200px |
| Map Caption1: | Location of Washington County in Arkansas |
| Subdivision Type: | Country |
| Subdivision Type1: | State |
| Subdivision Type2: | County |
| Subdivision Name2: | Washington |
| Established Title: | Established |
| Established Date: | 1829[1] |
| Unit Pref: | Imperial |
| Area Total Sq Mi: | 33.6 |
| Area Land Sq Mi: | 33.6 |
| Area Water Sq Mi: | 0.0 |
| Area Water Percent: | 0 |
| Population As Of: | 2000 |
| Population Total: | 655 |
| Population Density Sq Mi: | 19 |
| Elevation Ft: | 1053 |
| Coordinates: | 36.0542°N -94.4836°W |
| Timezone: | CST |
| Utc Offset: | -6 |
| Timezone Dst: | CDT |
| Utc Offset Dst: | -5 |
| Area Code: | 479 |
| Blank Name: | GNIS feature ID |
| Blank Info: | 69791 |
Illinois Township is one of thirty-seven townships in Washington County, Arkansas, USA.[2] As of the 2000 census, its total population was 655.
Illinois Township was established in 1829.[3]
According to the United States Census Bureau, Illinois Township covers an area of 33.6sqmi, all land.[2]
The township contains Beatty Cemetery, Harold Cemetery, Norwood Cemetery and Old Union Cemetery.