Harlem Township is located in Stephenson County, Illinois. As of the 2010 census, its population was 2,275 and it contained 981 housing units. It contains part of the census-designated place of Willow Lake.
Harlem is Township 27 North, Range 7 East of the Fourth Principal Meridian.
According to the 2010 census, the township has a total area of , of which (or 99.68%) is land and (or 0.32%) is water.
Tisdel Inn (Section 21) was built in 1852 by P.A. Tisdel along the Old State Road number 2, now Business U.S. Route 20. Frink, Walker & Company stage line, Chicago to Galena, used this road 1839 to 1854. The stone inn is now a residence.