For the 2021-22 season, Division III realigned basketball into 10 regions. Region 4 is a mix of teams from the former Atlantic and East regions. To find former East Region teams such as the Empire 8, Liberty League and SUNYAC, as well as former Atlantic Region teams from the Skyline Conference, check out Region 3.
| School | Location | Conference | Enrollment |
| Arcadia | Glenside, PA | MACF | 1866 |
| Baruch | New York, NY | CUNYAC | 12863 |
| Brooklyn | Brooklyn, NY | CUNYAC | 8865 |
| Bryn Athyn | Bryn Athyn, PA | UEC | 272 |
| Cairn | Langhorne, PA | UEC | 723 |
| CCNY | New York, NY | CUNYAC | 9421 |
| Clarks Summit | Clarks Summit, PA | UEC | 317 |
| Delaware Valley | Doylestown, PA | MACF | 1634 |
| DeSales | Center Valley, PA | MACF | 1664 |
| FDU-Florham | Madison, NJ | MACF | 2635 |
| Gallaudet | Washington, DC | UEC | 927 |
| Hunter | New York, NY | CUNYAC | 10764 |
| John Jay | New York, NY | CUNYAC | 9664 |
| Kean | Union, NJ | NJAC | 8475 |
| Keystone | La Plume, PA | UEC | 1087 |
| King's | Wilkes-Barre, PA | MACF | 1994 |
| Lancaster Bible | Lancaster, PA | UEC | 986 |
| Lebanon Valley | Annville, PA | MACF | 1611 |
| Lehman | Bronx, NY | CUNYAC | 5559 |
| Medgar Evers | Brooklyn, NY | CUNYAC | 3444 |
| Misericordia | Dallas, PA | MACF | 1330 |
| Montclair State | Upper Montclair, NJ | NJAC | 13221 |
| New Jersey City | Jersey City, NJ | NJAC | 4103 |
| New York University | New York, NY | UAA | 20950 |
| Notre Dame (Md.) | Baltimore, MD | UEC | 621 |
| Penn College | Williamsport, PA | UEC | 4766 |
| Penn State-Abington | Abington, PA | UEC | 2647 |
| Penn State-Berks | Reading, PA | UEC | 1908 |
| Penn State-Harrisburg | Middletown, PA | UEC | 1918 |
| Pratt | Brooklyn, NY | AEC | 4158 |
| Ramapo | Mahwah, NJ | NJAC | 5150 |
| Rosemont | Rosemont, PA | UEC | 385 |
| Rowan | Glassboro, NJ | NJAC | 7821 |
| Rutgers-Camden | Camden, NJ | NJAC | 5350 |
| Rutgers-Newark | Newark, NJ | NJAC | 4425 |
| St. Elizabeth | Morristown, NJ | UEC | 590 |
| St. Mary's (Md.) | St. Mary's City, MD | UEC | 1648 |
| Stevens | Hoboken, NJ | MACF | 2841 |
| Stockton | Pomona, NJ | NJAC | 5012 |
| TCNJ | Ewing, NJ | NJAC | 6040 |
| Valley Forge | Phoenixville, PA | UEC | 703 |
| William Paterson | Wayne, NJ | NJAC | 7220 |
| Wilson | Chambersburg, PA | UEC | 593 |
| York (N.Y.) | Jamaica, NY | CUNYAC | 4130 |