| S.N. | County | FIPS Code | County Seat | Est. | Population | Area (sq mi) | Area (km2) |
|---|---|---|---|---|---|---|---|
| 1 | Barnstable County | 1 | Barnstable | 1685 | 212,990 | 396 | 1,026 |
| 2 | Berkshire County | 3 | Pittsfield | 1761 | 124,944 | 931 | 2,411 |
| 3 | Bristol County | 5 | Taunton | 1685 | 565,217 | 556 | 1,440 |
| 4 | Dukes County | 7 | Edgartown | 1695 | 17,332 | 104 | 269 |
| 5 | Essex County | 9 | Salem, Lawrence | 1643 | 789,034 | 498 | 1,290 |
| 6 | Franklin County | 11 | Greenfield | 1811 | 70,180 | 702 | 1,818 |
| 7 | Hampden County | 13 | Springfield | 1812 | 466,372 | 618 | 1,601 |
| 8 | Hampshire County | 15 | Northampton | 1662 | 160,830 | 529 | 1,370 |
| 9 | Middlesex County | 17 | Lowell, Cambridge | 1643 | 1,611,699 | 824 | 2,134 |
| 10 | Nantucket County | 19 | Nantucket | 1695 | 11,399 | 48 | 124 |
| 11 | Norfolk County | 21 | Dedham | 1793 | 706,775 | 400 | 1,036 |
| 12 | Plymouth County | 23 | Brockton, Plymouth | 1685 | 521,202 | 661 | 1,712 |
| 13 | Suffolk County | 25 | Boston | 1643 | 803,907 | 58 | 150 |
| 14 | Worcester County | 27 | Worcester | 1731 | 830,622 | 1,513 | 3,919 |
