| Silverado Credit Union | California |
| Silvergate Bank | California |
| Silver Lake Bank | Kansas |
| Simmesport State Bank | Louisiana |
| Simmons First National Bank | Arkansas |
| Simplot Employees Credit Union | Idaho |
| Simply Service Federal Credit Union | South Dakota |
| Singing River Federal Credit Union | Mississippi |
| Sing Sing Employees Federal Credit Union | New York |
| Sioux Empire Federal Credit Union | South Dakota |
| Sioux Falls Federal Credit Union | South Dakota |
| Siouxland Federal Credit Union | Nebraska |
| Siouxland National Bank | Nebraska |
| Sioux Valley Community Credit Union | Iowa |
| Sioux Valley Co-op Federal Credit Union | South Dakota |
| SI Philadelphia Federal Credit Union | Pennsylvania |
| Siskiyou Central Credit Union | California |
| Sisseton-Wahpeton Federal Credit Union | South Dakota |
| Sister's Hospital Employees Federal Credit Union | New York |
| SIU Credit Union | Illinois |
| SIUE Credit Union | Illinois |
| Sixth Avenue Baptist Federal Credit Union | Alabama |
| SJH Employees' Credit Union | New Hampshire |
| SJN Bank of Kansas | Kansas |
| S & J School Employees Federal Credit Union | Ohio |
| Skagit Bank | Washington |
| Skel-Tex Credit Union | Texas |
| Skowhegan Savings Bank | Maine |
| Sky Federal Credit Union | Montana |
| Skyline Financial Federal Credit Union | Connecticut |
| SkyOne Federal Credit Union | California |
| Skyward Credit Union | Kansas |
| Sloan Public Schools Federal Credit Union | New York |
| Sloan State Bank | Iowa |
| SLO Credit Union | California |
| Slovak Savings Bank | Pennsylvania |
| Slovenian Savings and Loan Association of Canonsburg | Pennsylvania |
| Slovenian Savings and Loan Association of Franklin-Conemaugh | Pennsylvania |
| Smackover State Bank | Arkansas |
| Small Town Bank | Alabama |
| SmartBank | Tennessee |
| Smart Choice Credit Union | Tennessee |
| Smart Federal Credit Union | Ohio |
| Smart Financial Credit Union | Texas |
| SM Federal Credit Union | Pennsylvania |
| SM Federal Credit Union | Kansas |
| SMH Federal Credit Union | Illinois |
| Smith & Nephew Employees Credit Union | Tennessee |
| SMMH Federal Credit Union | Pennsylvania |
| SMSD Federal Credit Union | New York |
| SMW 104 Federal Credit Union | California |
| SMW Federal Credit Union | Minnesota |
| Snake River Federal Credit Union | Idaho |
| SNB Bank | Oklahoma |
| SnoCope Credit Union | Washington |
| Sno Falls Credit Union | Washington |
| SoCal Federal Credit Union | California |
| Social Security Credit Union | Alabama |
| SODES Federal Credit Union | South Dakota |
| Softite Community Federal Credit Union | Ohio |
| Solano First Federal Credit Union | California |
| Solarity Credit Union | Washington |
| Solera National Bank | Colorado |
| Solidarity Community Federal Credit Union | Indiana |
| Solon/Chagrin Falls Federal Credit Union | Ohio |
| Solon State Bank | Iowa |
| Solutions Federal Credit Union | New York |
| Solvay Bank | New York |
| Somerset Federal Credit Union | Massachusetts |
| Somerset Savings Bank | New Jersey |
| Somerset Trust Company | Pennsylvania |
| Somerville Mass Firefighters Federal Credit Union | Massachusetts |
| Somerville Municipal Federal Credit Union | Massachusetts |
| Somerville School Employees Federal Credit Union | Massachusetts |
| SonaBank | Virginia |
| Sonoma County Grange Credit Union | California |
| Sonoma Federal Credit Union | California |
| Sony San Diego Employees Federal Credit Union | California |
| Soo Co-op Credit Union | Michigan |
| Soo Line Credit Union | Minnesota |
| Sooner State Bank | Oklahoma |
| Sooper Credit Union | Colorado |
| Soo Select Credit Union | Minnesota |
| Soreng Employees Credit Union | Illinois |
| Sorg Bay West Federal Credit Union | Ohio |
| Sound Bank | North Carolina |
| Sound Banking Company | Washington |
| Sound Community Bank | Washington |
| Sound Credit Union | Washington |
| Soundview Financial Credit Union | Connecticut |
| SourceOne Credit Union | Illinois |
| South Atlantic Bank | South Carolina |
| South Atlantic Federal Credit Union | Florida |
| SouthBank | Alabama |
| South Bend Firefighters Federal Credit Union | Indiana |
| South Bend Post Office Credit Union | Indiana |
| Southbridge Credit Union | Massachusetts |
| Southbridge Savings Bank | Massachusetts |
| South Carolina Community Bank | South Carolina |
| South Carolina Federal Credit Union | South Carolina |