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- Jacob H. Chirhart: a Harris pioneer whose family crossed into Clay in 1865 Notable People
- Jacob Harris: the namesake of the prairie and the township Notable People
- Jacob Meyer: from the canal works to 460 acres — the settler who stayed on his first farm Notable People
- Jacob Shimp: "the last Jackson voter in St. Joseph county" — carried at county strength Notable People
- Jesse James never came: the pass-through legends, tested as a class Famous Stories & the Record
- Joe Donnelly: representative, senator, ambassador — of Granger Notable People
- John A. Zaehnle: Notre Dame commercial course, Civil War paymaster's clerk, and the Section 22 farm Notable People
- John Koker: the Swiss emigrant of 1824, by way of Clay to Harris Notable People
- John Lerner: born in Mishawaka, and printed so — a dairy farmer of Maple Front Farm Notable People
- John M. Shimp: "the Burr Oaks," and the presidency of the county farmers' mutual Notable People
- John W. Griffith: four years to a day under Sheridan, then Sunny Banks Farm Notable People
- Joseph County, the county's worked example, and the Granger layer named as GAP-C90-1 Controversies
- Joseph L. Krupp: blacksmith first, then 440 acres — and Susan Krupp, a patron in her own name Notable People
- Joseph Meyer: the second generation, superintending the 460 acres Notable People
- Journey Church: the Assemblies of God seat Churches & Religion
- Juday Creek Estates: the creek-side plat and its golf course Neighborhoods
- Juday Creek Golf Course: the Rogers family's public course, the 2024 fire, and the rebuild Sports
- Juday Creek: the ground's own water The Land
- Juday Creek: the monster that isn't, and the marvel that is Famous Stories & the Record