The PLSS data is modeled as a single composite network coverage that encompasses townships (area), sections (subarea), quarter sections, and half quarter section. If an indigenous people's reserve was present on the tax map, it was digitized to create subpolygons of the half-quarter section, and those polygons were attributed with the name of the reserve. Within this PLSS data set, a half-quarter section is the smallest polygon unit, except in cases where an Indigenous People's Reserve line is present.

The County's system of tax maps is based on the Illinois Public Land Survey System (PLSS). In the PLSS, each township is divided into 36 sections, and each section into four quarter-sections. A quarter-section is further divided into two tax map sheets, often called "pages". Each tax map (1/4 mile by 1/2 mile) represents the east or west half of one quarter-section, and typically there are eight tax maps per section.