Lee county's boundaries were finally set in 1839. Prior to that time, the area had been a part of Bond County and Clark County in 1818 (the year of Illinois' statehood), Putnam County in 1825 and Ogle County in 1836. It is named for Richard Henry Lee who signed the Declaration of Independence.
The county is located in northern Illinois with the Interstate 88/Interstate 39 interchange just to the north and east.