| Oneida County Federal Credit Union | New York |
| One Nevada Credit Union | Nevada |
| One Source Federal Credit Union | Texas |
| One South Bank | Florida |
| One Thirteen Credit Union | Colorado |
| One Twenty Credit Union | Massachusetts |
| OneUnited Bank | Massachusetts |
| One Vision Federal Credit Union | Indiana |
| OneWest Bank | California |
| One World Bank | Texas |
| Onomea Federal Credit Union | Hawaii |
| OnPoint Community Credit Union | Oregon |
| Ontario Montclair Schools Federal Credit Union | California |
| Ontario Public Employees Federal Credit Union | California |
| Ontario Shores Federal Credit Union | New York |
| Oostburg State Bank | Wisconsin |
| OPC Federal Credit Union | Oregon |
| Open Bank | California |
| Operating Engineers Local #148 Credit Union | Illinois |
| Operating Engineers Local Union #3 Federal Credit Union | California |
| OPP-Micolas Credit Union | Alabama |
| Opportunities Credit Union | Vermont |
| Opportunity Bank of Montana | Montana |
| OPS Employees Federal Credit Union | Pennsylvania |
| Optima Bank & Trust Company | New Hampshire |
| OptimumBank | Florida |
| Optum Bank | Utah |
| Opus Bank | California |
| Oral Federal Credit Union | Hawaii |
| Orange County Business Bank | California |
| Orange County's Credit Union | California |
| Orange County Teachers Credit Union | Texas |
| Orange County Trust Company | New York |
| Oregon Coast Bank | Oregon |
| Oregon Community Bank & Trust | Wisconsin |
| Oregon Community Credit Union | Oregon |
| Oregonians Credit Union | Oregon |
| Oregon Pacific Bank | Oregon |
| Oregon Pioneer Federal Credit Union | Oregon |
| Oregon State Credit Union | Oregon |
| Oregon Trail Bank | Wyoming |
| Orem City Employees Federal Credit Union | Utah |
| Organized Labor Credit Union | California |
| Origin Bank | Louisiana |
| Orion Federal Credit Union | Tennessee |
| Oritani Bank | New Jersey |
| Orlando Federal Credit Union | Florida |
| Orleans Parish Criminal Sheriff's Credit Union | Louisiana |
| ORLEX Government Employees Credit Union | Vermont |
| Ormsby State Bank | Minnesota |
| ORNL Federal Credit Union | Tennessee |
| Orrstown Bank | Pennsylvania |
| O & R Utilities Employees Federal Credit Union | New York |
| OSB Community Bank | Michigan |
| Oshkosh Community Credit Union | Wisconsin |
| Oshkosh Postal Employees Credit Union | Wisconsin |
| Oshkosh Truck Credit Union | Wisconsin |
| Osnova Ukrainian Federal Credit Union | Ohio |
| Ossian State Bank | Indiana |
| OSU Institute of Technology Federal Credit Union | Oklahoma |
| Oswego County Federal Credit Union | New York |
| Oswego Heritage Federal Credit Union | New York |
| Oswego Teachers Employees Federal Credit Union | New York |
| Oteen V.A. Federal Credit Union | North Carolina |
| Otero County Teachers Federal Credit Union | Colorado |
| Otero Federal Credit Union | New Mexico |
| Otis Federal Credit Union | Maine |
| OTS Employees Federal Credit Union | Hawaii |
| Ottawa Hiway Credit Union | Illinois |
| Ottawa Savings Bank | Illinois |
| Otter Tail Credit Union | Minnesota |
| Ouachita Independent Bank | Louisiana |
| Ouachita Valley Federal Credit Union | Louisiana |
| Ouachita Valley Health System Federal Credit Union | Arkansas |
| OU Federal Credit Union | Oklahoma |
| Our Community Bank | Indiana |
| Our Community Credit Union | Washington |
| Our Credit Union | Michigan |
| Our Family Social Credit Union | Nebraska |
| Our Lady of Angels Federal Credit Union | Ohio |
| Our Lady of Good Hope Credit Union | Wisconsin |
| Our Lady of Snows Credit Union | Missouri |
| Our Lady of the Angels Federal Credit Union | Massachusetts |
| Our Lady of Victory Institutions Federal Credit Union | New York |
| Our Mother of Mercy Parish Houston Federal Credit Union | Texas |
| Our Sunday Visitor Employees Federal Credit Union | Indiana |
| Outreach Community Federal Credit Union | Tennessee |
| Owen County State Bank | Indiana |
| Owensboro Federal Credit Union | Kentucky |
| Owingsville Banking Company | Kentucky |
| Owosso WBC Federal Credit Union | Michigan |
| Oxford Bank | Michigan |
| Oxford Bank & Trust | Illinois |
| Oxford Credit Union | North Carolina |
| Oxford Federal Credit Union | Maine |
| Oxford University Bank | Mississippi |
| Ozark Bank | Missouri |
| Ozark Federal Credit Union | Missouri |
| Ozarks Federal Savings and Loan Association | Missouri |
| Ozona Bank | Texas |