| Surnames | Time Period | Researcher |
| O’Brien | 1890 - ? | Kerry O’Brien |
| Odione | 1945 - now | Jim DeWitt |
| Ogden | Heidi Ogden-Wicks | |
| Oldfather | 1897 - now | Allen W. Davis |
| O'Leary | Richard C. O'Leary | |
| Oliver | 1885 - now | Richard Broughton |
| Oliver | 1860 - 1900 | Kathryn Andres |
| Oliver | 1894 | Tammie |
| O'Loughlin | 1850 - now | John O'Loughlin |
| Ostendorf | 1875 - 1888 | Susan Thompson |
| Owens | 1940 | Virginia Lawson Long |
| Padgett | 1850 - now | Earl C. Padgett |
| Palmer | c 1880s | Tom Green |
| Parcells | 1849 - 1880 | Kay Wilson |
| Parris | . | Florence (Parris) Hicks |
| Patrick | c1900 - 1948 | Ann Stansbarger |
| Patten | 1875 - 1920 | Judy Stuck |
| Paulk | . | Vickey-Arlene Collins |
| Pearson | 1860 - 1954 | John E. Pearson III |
| Pearson | 1875 - 1990 | Carol Mowery |
| Peltzer | 1880 - 1999 | Douglas B. Ayer |
| Pennington | 1800 - now | Gay Lynn Garcia |
| Penny | . | Karleen (Penny) Street |
| Perkins | 1900 - 1921 | Alice Deaton |
| Petitjean | . | Olin Petitjean |
| Pfaff | 1880 - now | Jim Pfaff |
| Phelps | . | Anne Townsend |
| Philips | 1870 - 1950 | Deb Shillo |
| Phillips | 1895 | Roger Phillips |
| Phillips | 1900 - 1910 | Marlene J. Shaw |
| Pieplow | 1945 | Sue Anne Coyle |
| Pierce | 1880s - 1920s | Carol E. King |
| Pierce | 1875 - c1900 | Don Henricks |
| Pierce | 1930 - now | Otto K. Land |
| Pigg | 1880s - 1920 | Laurie Lewis |
| Pinson | Karen "Kari" Muschetto-Uhlman | |
| Pitcher | 1880 - 1940 | Edward Pitcher |
| Pitts | 1875 - c1925 | Elise C. Morris |
| Pluess | . | Gary Haas |
| Poffenberger | 1910 - | Sandra Jones |
| Polson | 1940 - 1950 | Laralea Stehwein Whetstine |
| Pompa | 1930 - now | Sonya Brock |
| Porth | 1890 - 1918 | Delores Mather |
| Posch | 1880 - 1999 | Douglas B. Ayer |
| Postlethwait | 1860 - now | Michael Joe Postlethwait |
| Potts | mid-1800s | Ethel Stevens |
| Potts | 1906 - now | George Potts |
| Pratt | 1850 - 1940 | Preston McCall |
| Pray | 1880 - 1915 | Cheryl Behrend |
| Priddy | 1850 - 1960 | Bob L. Priddy |
| Pritchard | . | Kim Duren |
| Puett | 1900 - 1910 | Sandy Cotter |
| Pullar | 1865 - 1880 | Gordon L. Pullar |
| Pullen | 1873 - 1914 | Arlene (Pullen)Smith |
| Purcell | 1871 - 1939 | Martha J. Swaim Wyckoff |
| Quackenbush | 1990 - 2003 | Richard Quackenbush |
| Quillen | 1920 - present | Suann Moore |
| Rambo | 1835 - | Mary Klassen |
| Randall | ? | Cheryl Herrera |
| Rattley | 1900 - 1920 | Robert Jackson |
| Rauh | 1884 - 1889 | Kathy Heinz |
| Rausch | 1910 - ? | Patt Rausch |
| Rausch | 1870 - present | Dave Williams |
| Rausch | 1880 - 1950 | M. Bolster |
| Raymond | 1860 - now | Marsha R. Faulkner |
| Rector | 1900 - now | Carmel |
| Redfield | 1870 - now | Ray Downing |
| Reed | 1900 - 1940 | Cheryl Behrend |
| Reed | 1950 - 1960 | C. Stratton |
| Reeves | ? - 1942 | Richard Reeves |
| Reichert | 1890 - now | Dawn Wyer |
| Reilly | ? - 1973 | Marcella Piersall |
| Reimer | 1920 - now | Nadine Brinson |
| Renshaw | 1900 | Jean Renshaw |
| Revelle | 1880 - 1950 | Alice Reville Tomlin |
| Reynolds | 1950 - 1960 | Freddie Reynolds |
| Reynolds | . | Natalie |
| Rhodes | . | Kim M. Estes |
| Rhodes/Rhoades | 1870 - c1930 | S. Viehweg |
| Richardson | 1910 - 1920 | Lavena Crawford |
| Richey | 1900 - 1920 | Robert Jackson |
| Ridgway | . | Jenell Rector Cremeans |
| Rittenour | 1901 - 1932 | Ruth Kuntz |
| Roach | 1916 | Barbara Rich |
| Roadenbaugh | . | Vickey-Arlene Collins |
| Robey | 1880 - now | Sharon Robey Bambara |
| Robinson | 1950 - now | Verna Bice |
| Rollin | 1880 - 1920 | Richard Rollin |
| Rollings | 1990 - now | Nelda Dimmick |
| Roman | ? | David Salas |
| Romine | 1840 - 1860 | Jan Menhusen Smock |
| Ronsick | . | Uwe Mylatz |
| Rose | 1930s | L.G. Robinson |
| Ross | 1861 | Kevin Sullivan |
| Roth | 1860 | Joan R Gallagher |
| Rouse | 1874 | Muriel Waldron |
| Rouse | 1880 - 1929 | Betsy Erwin |
| Routh | 1883 - now | Joyce (Routh) Willhoit |
| Row | 1910 - now | Terry Row |
| Row | 1910 - now | Lori Parks |
| Rowden | 1880 - now | Gary G. Rowden |
| Royse | 1890s | Joshua Griffen |
| Ruddle | 1911 - 1930 | Clara Rae Ruddle |
| Rush | 1880s - ? | Glenda Cashmer |
| Russell | 1940 - now | Harold E. Hansen |
| Ryder | 1880 - 1920 | James Lane |