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County research and study

Marshall County, Illinois

Use a county profile as a source-reading exercise or the geographic context for your own research. Keep the county FIPS identifier with your notes so that similarly named places in different states are not mixed.

County FIPS17123Five-digit Census identifier
Population11,473July 1, 2025 estimate
Land area386.82 mi²2025 Gazetteer
Population per land mi²29.66Calculated from the cited population and land area

Identify the right place

Marshall County is a county or county equivalent in Illinois. Its five-digit FIPS code is 17123; preserve the leading zero when storing county codes as text. The Gazetteer lists 11.72 square miles of water and a representative point at 41.031119, -89.342371. That point identifies the geography; it is not a street address or a site boundary.

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County research and study checklist

  1. Write a specific research question before summarizing sources.
  2. Separate a Census estimate from an exact count or a current forecast.
  3. Cite the dataset and year next to every number in your notes.

The figures describe the county; they are not an evaluation of schools or an estimate of educational outcomes.

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Sources and interpretation

Geography: 2025 U.S. Census Gazetteer. Population: Vintage 2025 estimates, July 1, 2025. County equivalents include parishes, boroughs, independent cities and planning regions. Puerto Rico population is not supplied by this population file.

Population is an estimate, not a live count. Gazetteer land and water measures describe the geographic area; they do not measure service availability, households, businesses or market demand. Match the FIPS code and source vintage when joining another dataset.

More county references in Illinois

Browse all 102 county equivalents in Illinois