| Surnames | Time Period | Researcher |
| Jackson | 1938 | Lori Klassen |
| Jacques | 1900 - now | Cristie Maure |
| Jahn | 1850 - 1900 | Dave Johnson |
| Jamison | 1913 | Pat Grimm |
| Jansen | 1918 - now | Barbara Tallett |
| Jansen | 1879 - now | Val Jansen |
| Jennings | 1955 - 1958 | John Jennings |
| Jewell | 1890 - 1936 | Susan Doell |
| Jewell | 1880 - 1930 | Carol Jo Hossle |
| Jockers | 1900 - now | Sandra J. Kelley |
| Johnson | 1870 - now | Jan LaMotte |
| Jones | 1880 - now | Judy |
| Josien | 1930s | Robin McDuffie |
| Judah | 1860 - now | Herb Ragle |
| Kabler | 1870 - now | Carol McCoy |
| Kasmirsky | 1870s - 1880s | Michael Hamersky |
| Kaub | 1908 | Sandra Kaub |
| Kamen | 1900 - 1910 | P. Reinstein |
| Kamenensky | 1900 - 1910 | P. Reinstein |
| Kaufman | 1890 - 1920 | Erika Jones |
| Kearney | 1889 - 1910 | Kathryn Andres |
| Kehl | . | Kevin L. Kehl |
| Kennedy | 1870 - 1950 | Deb Shillo |
| Kennedy | 1910 - now | John E. Bartos |
| Kephart | 1940 | Helen Hudson |
| Kerr | 1890s | Jackie Mastey |
| Kersting | 1800 - now | David Kersting |
| Kinahan | . | Harry Kodis |
| King | 1970 - 1990 | Karen Finney |
| Kinman | 1890 - now | Leroy Gailey |
| Kinney | 1920 | Robert Jackson |
| Kinsall | ? - 1967 | Janice Cain |
| Kirkland | 1930s - now | Neal Kirkland |
| Kiser | 1900 - 1975 | Carol Mowery |
| Kisley | . | Sharon Pierpont |
| Kittle, John | . | Sandra Thompson |
| Klaassen | 1907 - now | Linda Shields |
| Knapp | 1904 - 1938 | Cherie Knapp Goldberg |
| Knifley | 1860 - now | Gerry Knifley |
| Knight | c1895 - 1945 | Ava Leaverton |
| Knight | . | Richard Russell |
| Knoblauch | 1870s - 1900 | Michael Hamersky |
| Knobloch | 1870s - 1900 | Michael Hamersky |
| Knoblouch | 1883 - 1970 | Walter Thomas E. Cochran |
| Knofflock | c1875 - ? | Treisa Dugas |
| Koenigs | 1860 - 2000 | Chris Koenigs |
| Koontz | . | Jenell Rector Cremeans |
| Kraus | 1870s - 1900 | Michael Hamersky |
| Kunzel | 1880 - 1920 | Laura Cooksey |
| Kurtze | 1800 - 1900 | Taylor Smith |
| Labounty | 1800 - new | Belinda Reynolds |
| Laessig | 1895 -1945 | Craig Laessig |
| Lammey | . | Mike Kimmen Jr. |
| Lampl | 1880s - 1940s | Suzanne Lampl |
| Land | . | Ric Land |
| Langley | 1915 - 1920 | Barbara Chisler |
| LaRue | 1874 - 1898 | Ron Levagood |
| Lassen | 1900 - 1920 | Vicki Tate |
| Lassig | 1895 -1945 | Craig Laessig |
| Laughlin | 1850 - now | John O'Loughlin |
| Lawless | 1860 - now | Marsha R. Faulkner |
| Lawson | 1880 - 1940 | Lonnie Lawson |
| Leal | 1960 - 1980 | Linda Cantrell |
| Leaverton | . | Shirley Leaverton |
| Lee | 1915 - 1920 | Barbara Chisler |
| Lessig | 1895 -1945 | Craig Laessig |
| Levagood | 1874 - 1882 | Ron Levagood |
| Lewellen | Don Lewellen | |
| Liggett | 1880 - now | Joe Williams |
| Lill | 1880 - now | Debra Kasper |
| Lilley | 1920s | Janet Matschull |
| Linfor | . | Lynette Trainer |
| Lingo | - 1908 | Mike Graham |
| Littleton | 1900 - now | Bea Littleton |
| Lively | 1900 - 1931 | Inez Rambo Berg |
| Livingston | 1930s | Robin McDuffie |
| Livingston | 1880 - | Glenda Nighswonger |
| Loch | . | Christopher Loch |
| Loehr | 1870s - 1900 | Michael Hamersky |
| Logue | 1860 - 1910 | Norman Logue |
| Longwill | 1880 - 1898 | Kim Campbell |
| Loudenback | 1880 - 1930 | Loudenback |
| Loudenslager | 1860 - 1960 | Debbie Duley |
| Loveland | 1960 - now | Pearl Thomas |
| Lovern | 1850 - now | Tresa McVay |
| Lutz | ? - 1940s | Robert Frederick |
| Lynes | 1860 - 1999 | David Parks |
| Lynn | 1861 - 1926 | Michael R. Stuckey |
| Lyon | 1868 - 1902 | Judson Crow, Sr. |