Dennison is an unincorporated community in Wabash Township in the northeast corner of Clark County, Illinois, east of Illinois Route 1 and north of Interstate 70. Geography Dennison is located at 39°27'39" North, 87°35'52" West (39.4608688, -87.5978025). References External links Dennison History at Genealogy Trails. Unincorporated communities in Clark County, Illinois Unincorporated communities in Illinois