| Nourish Pierce CountyEIN 91-1198391 | Human Services | WA | $11,368,057Mid-sized | 92.20 |
| Noyes Home for ChildrenEIN 44-0563788 | Human Services | MO | $2,369,119Small | 80.79 |
| NPH USAEIN 65-1229309 | Human Services | IL | $18,458,495Large | 87.23 |
| NPower Inc.EIN 13-4145441 | Human Services | NY | $11,876,339Mid-sized | 95.50 |
| NPREIN 52-0907625 | Arts, Culture, Humanities | DC | $222,910,067Large | 84.25 |
| NumbersUSA Education and Research Foundation EIN 47-0865426 | Human and Civil Rights | VA | $6,623,333Mid-sized | 98.23 |
| Nurse-Family PartnershipEIN 20-0234163 | Human Services | CO | $19,101,215Large | 95.10 |
| Nurses for Newborns EIN 43-1601329 | Human Services | MO | $4,296,133Mid-sized | 90.29 |
| Nuru InternationalEIN 26-1250716 | International | CA | $5,795,736Mid-sized | 93.74 |
| Nutmeg Big Brothers Big SistersEIN 06-0850379 | Human Services | CT | $1,680,191Small | 91.06 |
| NW Children's FoundationEIN 91-1314318 | Human Services | WA | $1,390,355Small | 86.10 |
| Nyaka Aids Orphans ProjectEIN 35-2153719 | International | MI | $1,384,998Small | 91.10 |
| NYC Outward Bound SchoolsEIN 13-3471084 | Education | NY | $6,541,364Mid-sized | 97.26 |
| Oakland East Bay SymphonyEIN 94-3081554 | Arts, Culture, Humanities | CA | $2,813,517Small | 86.89 |
| Oakland ZooEIN 94-1687847 | Animals | CA | $17,255,821Large | 90.19 |
| Oasis CenterEIN 62-0968273 | Health | TN | $4,868,963Mid-sized | 95.20 |
| Occidental Arts and Ecology CenterEIN 68-0359676 | Environment | CA | $1,944,634Small | 77.79 |
| Ocean AllianceEIN 22-2573677 | Animals | MA | $765,223Small | 75.38 |
| Ocean ConservancyEIN 23-7245152 | Environment | DC | $23,984,534Large | 91.97 |
| Ocean Discovery InstituteEIN 33-0862531 | Education | CA | $1,771,417Small | 90.15 |
| Ocean InstituteEIN 33-0203488 | Education | CA | $6,496,221Mid-sized | 86.98 |
| Ocean Research & Conservation AssociationEIN 20-0901011 | Environment | FL | $1,613,797Small | 72.08 |
| OceanaEIN 51-0401308 | Environment | DC | $37,880,581Large | 94.11 |
| Officers' Christian FellowshipEIN 38-1415401 | Religion | CO | $4,426,565Mid-sized | 91.82 |
| Ohio City IncorporatedEIN 34-1372076 | Community Development | OH | $1,197,417Small | 85.47 |
| Ohio Environmental CouncilEIN 31-0805578 | Environment | OH | $2,085,734Small | 83.94 |
| Ohio United WayEIN 31-0619209 | Community Development | OH | $872,862Small | 83.50 |
| Ohr Somayach InternationalEIN 13-3503155 | Religion | NY | $4,063,985Mid-sized | 70.25 |
| Ohr Torah Stone Colleges and Graduate ProgramsEIN 13-3275531 | Religion | NY | $5,013,619Mid-sized | 81.38 |
| Ojai Music FestivalEIN 95-2122508 | Arts, Culture, Humanities | CA | $1,980,707Small | 79.08 |
| Okizu FoundationEIN 68-0291178 | Health | CA | $2,017,839Small | 86.23 |
| Oklahoma Arts InstituteEIN 73-1021165 | Education | OK | $2,394,342Small | 86.44 |
| Oklahoma Baptist Homes for ChildrenEIN 73-1435473 | Human Services | OK | $13,396,030Mid-sized | 82.36 |
| Oklahoma Center for NonprofitsEIN 73-1501645 | Community Development | OK | $1,690,215Small | 90.25 |
| Oklahoma City Art MuseumEIN 73-0528431 | Arts, Culture, Humanities | OK | $8,417,047Mid-sized | 86.56 |
| Oklahoma City BalletEIN 23-7003520 | Arts, Culture, Humanities | OK | $3,575,680Mid-sized | 80.71 |
| Oklahoma City Boathouse FoundationEIN 20-1837237 | Human Services | OK | $11,652,313Mid-sized | 78.06 |
| Oklahoma Contemporary Arts CenterEIN 73-1334271 | Arts, Culture, Humanities | OK | $2,546,424Small | 77.84 |
| Oklahoma Council of Public AffairsEIN 73-1436375 | Research and Public Policy | OK | $2,173,852Small | 75.57 |
| Oklahoma Humane SocietyEIN 20-8446621 | Animals | OK | $3,137,627Small | 89.38 |
| Oklahoma Institute for Child AdvocacyEIN 73-1192768 | Human Services | OK | $894,750Small | 80.87 |
| Oklahoma Medical Research FoundationEIN 73-0580274 | Health | OK | $75,113,337Large | 93.94 |
| Olbrich Botanical SocietyEIN 39-1357247 | Environment | WI | $2,874,467Small | 88.26 |
| Old Dartmouth Historical Society/New Bedford Whaling MuseumEIN 04-2104805 | Arts, Culture, Humanities | MA | $4,527,585Mid-sized | 93.25 |
| Old Dominion Athletic FoundationEIN 54-6051933 | Education | VA | $7,930,953Mid-sized | 89.39 |
| Old Globe TheatreEIN 95-1543396 | Arts, Culture, Humanities | CA | $25,227,945Large | 90.59 |
| Old Newsboys' Goodfellow Fund of DetroitEIN 38-6061491 | Human Services | MI | $1,763,242Small | 91.22 |
| Old Savannah City MissionEIN 31-1810829 | Human Services | GA | $1,200,200Small | 71.74 |
| Oldways Preservation TrustEIN 04-3031978 | Research and Public Policy | MA | $2,135,083Small | 85.00 |
| Ole Miss Athletics FoundationEIN 64-0474850 | Education | MS | $41,714,200Large | 93.73 |
| Oliver Gospel MissionEIN 57-6027750 | Human Services | SC | $3,388,839Small | 88.44 |
| Oliver ScholarsEIN 13-3248876 | Education | NY | $4,018,563Mid-sized | 96.97 |
| Olympia Union Gospel MissionEIN 91-1680748 | Human Services | WA | $1,823,684Small | 70.48 |
| Omaha Community PlayhouseEIN 47-0399856 | Arts, Culture, Humanities | NE | $4,315,647Mid-sized | 80.52 |
| Omaha Performing ArtsEIN 47-0832480 | Arts, Culture, Humanities | NE | $18,775,491Large | 85.12 |
| Omaha SymphonyEIN 47-6039304 | Arts, Culture, Humanities | NE | $7,876,033Mid-sized | 95.83 |
| Omaha's Henry Doorly ZooEIN 47-0469782 | Animals | NE | $46,482,503Large | 87.05 |
| On PointEIN 68-0533402 | Human Services | TN | $1,327,471Small | 89.10 |
| On the BoardsEIN 91-1081983 | Arts, Culture, Humanities | WA | $1,635,622Small | 90.81 |
| On the MoveEIN 75-3149095 | Education | CA | $4,571,332Mid-sized | 90.58 |