Jefferson “J. W.” Jackson: 30-something ex-Boston cop, in Martha’s Vineyard, Massachusetts, by Philip Craig

Jolene Jackson: free-lance journalist, whose trouble starts whenever she goes home to Kickapoo, Texas, by Paula Boyd

Kane Jackson: industrial espionage expert and detective, by William Arden (Dennis Lynds)

Matt Jacob: former social worker, now a private investigator with a drug problem, in Boston, Massachussets, by Zachary Klein

Calista Jacobs: illustrator of children’s books in Cambridge, Massachusetts, by Kathryn Lasky Knight

Miles Jacoby: boxer turned private investigator in New York City, by Robert J. Randisi

Milan Jacovich: blue-collar Slovenian private eye with a master’s degree in Cleveland, Ohio, by Les Roberts

Daniel Jacquot: former rugby player, now a homicide chief inspector, in Marseilles, France, by Martin O’Brien

Jo Jacuzzo: charismatic lesbian in Buffalo, New York, by Anne Seale

Amanda Jaffe: attorney in Portland, Oregon, by Philip Margolin

Cassidy James: lesbian private investigator in the fictional town of Cedar Hills (near the Southern Oregon Coast about 350 miles from Portland), by Kate Calloway

Cassandra James: professor and administrator at St. Etheldreda’s College, in Cambridge, England, in the Cambridge mysteries by Christine Poulson

Dewey James: 60-something small town librarian in Hamilton, Kentucky, by Kate Morgan

Gemma James: Scotland Yard sergeant, Duncan Kincaid, a superintendent, in London, England, by Deborah Crombie

Jessica “Jesse” James: investigative reporter in Rochester, New York, by Meg O’Brien

Lis James: journalist turned public relations officer for a mental health center, in Houston, Texas, by Karen Hanson Stuyck

Mira James: assistant librarian and part-time reporter, in Battle Lake, Minnesota, in the Murder-by-Month mysteries, by Jess Lourey

Cass Jameson: criminal lawyer in Brooklyn, New York, by Carolyn Wheat

Frank Janek: NYPD homicide detective in New York City, by William Bayer

Cliff Janeway: cop and rare book expert, in Denver, Colorado, by John Dunning

Willa Jansson: law student, then lawyer, and a child of idealistic, left-wing parents, in San Francisco, California, by Lisa Matera

Ben January: surgeon and music teacher, in 1830s New Orleans, Louisiana, by Barbara Hambly

Oliver Jardine: police detective, and Theresa Fortunato, tarot-reading psychic, in Los Angeles, California, by Kate Green

Elena Jarvis: wise-cracking police detective, in Los Santos, Texas, by Nancy Herndon (Nancy Fairbanks)

Jarrod Jarvis: former child-star and gay amateur sleuth, in Los Angeles, California, and London, England, by Rick Copp

Jazz Jasper: American safari guide in Kenya, by Karin McQuillan

Kate Jasper: vegetarian and gag-gift wholesaler, in Marin County, California, by Jaqueline Girdner

Earl Jazine and Carl Crader, computer cops in the future, by Edward D. Hoch

Tal Jefferson: defeated attorney who escapes the big city and returns to Wynnton, South Carolina, the small town where she was raised, by Tracy Dunham

Mrs. Jeffries: housekeeper for Inspector Witherspoon, a policeman in London, England, in the Victorian mysteries by Emily Brightwell

Harriet Jeffries: photographer, and John Sanders, a police detective, in Toronto, Ontario, Canada, by Medora Sale (Caroline Roe)

Jane Jeffry: suburban housewife and sleuth in Chicago, Illinois, by Jill Churchill

Miss Jenkins, a “Gal Friday”, and Jake Rossiter, a private investigator, in post-World War II Seattle, Washington, by Curt Colbert

Elise Jenkins: reporter for the Ocean Point Weekly, and Mitch Burns, a police detective, in Ocean Point, New Jersey, by Laura Bradford

Glyndwr Jenkins: and David Brade, police detectives in Cardiff, Wales, by David Craig (Bill James)

Harry Jenkins: lawyer in a small wills and estates firm in Toronto, Ontario, Canada, in the Osgoode Trilogy, by Mary E. Martin 

Matthew Jenkyn: 15th century soldier and double agent spy, in England, by P.C. Doherty

Jimmy Jenner: pensioned-off cop with a wooden leg in the Stoke Newington section of London, England, by John Milne

Sergeant Alex Jensen: state trooper, and Jessie Arnold, a dog sled racer, in Anchorage, Alaska, by Sue Henry

Georgia Jensen: historical researcher turn sleuth, by P.A. Stelzer

Ophelia Jensen: reluctant witch who is a librarian, and her grandmother Abby, in a small town in Iowa, by Shirley Damsgaard

Martin Jerrold: lieutenant in the British Navy in the early 1800s, in the Reluctant Adventures trilogy, by Edwin Thomas

John Jericho: artist and crusader, by Hugh Pentecost (Judson Philips)

Jesus Creek: an eccentric small town in Tennessee, by Deborah Adams

Jethro: cat burglar recruited by MI5, in post-WWII London, England, by Tony Broadbent

Sonchai Jitpleecheep: police detective in Bangkok, Thailand, by John Burdett

Sister Joan: investigative nun in Cornwall, England, by Veronica Black

Ron Jobeman: former clergyman managing fast-food restaurants in Hollywood, California, by Thomas H. Griffith

Gertie Johnson: 60-something sleuth in the Upper Peninsula of Michigan, in the Yooper mysteries by Deb Baker

Hilda Johansson: young immigrant from Sweden working as a servant for the Studebaker family around the turn-of-the-19th century in South Bend, Indiana, by Jeanne M. Dams

John the Eunuch: Lord Chamberlain to the Emperor Justinian in Constantinople in 537, by Mary Reed and Eric Mayer

Coffin Ed Johnson and Grave Digger Jones, detectives in Harlem, living in Astoria, Queens, New York, by Chester Himes

Frank Johnson: private investigator in Virginia and then West Virginia, by Ed Lynskey

Johnson Johnson: British agent and yachtsman on the “Dolly” by Dorothy Dunnett

Dr. Sam. Johnson: real-life 18th-century lexicographer and sage, in London, England, by Lillian De La Torre

Mr. Jones: bodyguard and private investigator, and Carly Wagner, a Texas congresswoman, in Washington DC, by Jo-Ann Power

Abel Jones: federal agent during the American Civil War, by Owen Parry

Casey Jones: unlicensed private eye in North Carolina, by Katy Munger

Cleopatra Jones: special agent fighting drug trafficking, by Ron Goulart

Demary Jones: owner of Confidential Research, specializing in genealogy and historical research, in Seattle, Washington, by E.L. Larken

Fremont Jones: owner of a typewriter service in turn-of-the-19th-century San Francisco, California, by Dianne Day

Hannibal Jones: in Washington, DC, by Austin S. Camacho

Grave Digger Jones and Coffin Ed Johnson, detectives in Harlem, living in Astoria, Queens, New York, by Chester Himes

Jupiter Jones: Harvard fine arts instructor and amateur sleuth, in Boston, Massachusetts, by Timothy Fuller

Lena Jones: of Desert Investigations in Scottsdale, Arizona, by Betty Webb

Ridley Jones: freelance writer in New York City, by Lisa Unger (Lisa Miscione)

Sam Jones: sculptor in Camden Town, London, England, by Lauren Henderson

Texana Jones: trading post owner in the Big Bend Region of Texas, by Allana Martin

John Jordan: prison chaplain at the Potter Correctional Institution in north Florida, by Michael Lister

Miss Julia: elderly widow in Abbotsford, North Carolina, by Ann B. Ross

Ben Jurnet: detective inspector, raised a Unitarian, perhaps of Jewish descent, in Norfolk, England, by S.T. Haymon

Richard Jury: Scotland Yard investigator based in London, England, by Martha Grimes

Benjamin Justice: reporter in Los Angeles, California, by John Morgan Wilson

Charlotte Justice: black homicide detective in Los Angeles, California, by Paula L. Woods