The roots of Immaculate Conception parish stretch back to the mid-1800's when territory which now includes Highland Park was held by the Potowatomi Indians. The occupants of the area were Indians, and some white traders who were licensed by the government to operate within the region. On September 26, 1833, the U.S. government concluded a treaty with the Potowatomi (Treaty of Chicago) which included a tract of land along the shore of Lake Michigan north of the town of Kenilworth, plus all of Deerfield Township. The treaty was signed in Chicago which was then a settlement of some 350 people. According to the treaty, the Indian title was to expire February 21, 1835, with the Indians free to remain in the area until August, 1836. A contract for the first government survey of the area was issued November 21, 1836, which made land grants possible for the first time. There is some question as to the name of the first settler in the area; however John K. Clarke, better known as "Indian" Clarke, is regarded as the first permanent white trapper. Captain Daniel Wright, who lived on the Des Plaines River about 1834 or 1835, is reported to be the first white resident of the area. But in the region covered by Deerfield township, Michael Meahen was the first resident (1835), followed by Jacob Cadwell in the Spring of 1836. The first entry for land within the modern limits of Highland Park was made by John and Peter Fennerty in 1841 for an area bounded roughly by present day Green Bay Road on the west, Lake Michigan on the east, Elm Place (or Vine Avenue) on the north, and Lincoln Avenue on the south.

The Highland Park area was under the jurisdiction of many governments even before the treaty with the Potowatomi. At different times both French and British flags were flown over the area. At separate points it was part of a county of the State of Virginia, part of the Northwest Territory, and part of the Territory of Wisconsin. After Illinois won its statehood in 1818, the area went through a series of changes in County governments. First it was part of Peoria County, then Cook County, and then McHenry County. In 1839 McHenry County was divided into present day McHenry and Lake Counties. Finally, in 1850, Deerfield Township was created.