| County | FIPS Code | County Seat | Smithsonian Trinomial | Established in | Population | Area (sq mi) | Area (km2) |
|---|---|---|---|---|---|---|---|
| Adams County | 1 | Natchez | AD | 1799 | 32,297 | 460 | 1,191 |
| Alcorn County | 3 | Corinth | AL | 1870 | 37,057 | 400 | 1,036 |
| Amite County | 5 | Liberty | AM | 1809 | 13,131 | 730 | 1,891 |
| Attala County | 7 | Kosciusko | AT | 1833 | 19,564 | 735 | 1,904 |
| Benton County | 9 | Ashland | BE | 1870 | 8,729 | 407 | 1,054 |
| Bolivar County | 11 | Cleveland, Rosedale | BO | 1836 | 34,145 | 876 | 2,269 |
| Calhoun County | 13 | Pittsboro | CN | 1852 | 14,962 | 587 | 1,520 |
| Carroll County | 15 | Vaiden, Carrollton | CA | 1833 | 10,597 | 628 | 1,627 |
| Chickasaw County | 17 | Houston, Okolona | CS | 1836 | 17,392 | 502 | 1,300 |
| Choctaw County | 19 | Ackerman | CH | 1833 | 8,547 | 419 | 1,085 |
| Claiborne County | 21 | Port Gibson | CB | 1802 | 9,604 | 487 | 1,261 |
| Clarke County | 23 | Quitman | CK | 1833 | 16,732 | 691 | 1,790 |
| Clay County | 25 | West Point | CL | 1871 | 20,634 | 409 | 1,059 |
| Coahoma County | 27 | Clarksdale | CO | 1836 | 26,151 | 554 | 1,435 |
| Copiah County | 29 | Hazlehurst | CP | 1823 | 29,449 | 777 | 2,012 |
| Covington County | 31 | Collins | CV | 1819 | 19,568 | 414 | 1,072 |
| DeSoto County | 33 | Hernando | DS | 1836 | 161,252 | 478 | 1,238 |
| Forrest County | 35 | Hattiesburg | FO | 1906 | 74,934 | 467 | 1,210 |
| Franklin County | 37 | Meadville | FR | 1809 | 8,118 | 565 | 1,463 |
| George County | 39 | Lucedale | GE | 1910 | 22,578 | 478 | 1,238 |
| Greene County | 41 | Leakesville | GN | 1811 | 14,400 | 713 | 1,847 |
| Grenada County | 43 | Grenada | GR | 1870 | 21,906 | 422 | 1,093 |
| Hancock County | 45 | Bay Saint Louis | HA | 1812 | 43,929 | 477 | 1,235 |
| Harrison County | 47 | Gulfport, Biloxi | HR | 1841 | 187,105 | 581 | 1,505 |
| Hinds County | 49 | Jackson, Raymond | HI | 1821 | 245,285 | 869 | 2,251 |
| Holmes County | 51 | Lexington | HO | 1833 | 19,198 | 756 | 1,958 |
| Humphreys County | 53 | Belzoni | HU | 1918 | 9,375 | 418 | 1,083 |
| Issaquena County | 55 | Mayersville | IS | 1844 | 1,406 | 413 | 1,070 |
| Itawamba County | 57 | Fulton | IT | 1836 | 23,401 | 532 | 1,378 |
| Jackson County | 59 | Pascagoula | JA | 1812 | 139,668 | 727 | 1,883 |
| Jasper County | 61 | Bay Springs, Paulding | JS | 1833 | 17,062 | 676 | 1,751 |
| Jefferson County | 63 | Fayette | JE | 1799 | 7,726 | 519 | 1,344 |
| Jefferson Davis County | 65 | Prentiss | JD | 1906 | 12,487 | 408 | 1,057 |
| Jones County | 67 | Laurel, Ellisville | JO | 1826 | 67,761 | 694 | 1,797 |
| Kemper County | 69 | De Kalb | KE | 1833 | 10,456 | 766 | 1,984 |
| Lafayette County | 71 | Oxford | LA | 1836 | 47,351 | 631 | 1,634 |
| Lamar County | 73 | Purvis | LM | 1904 | 55,658 | 497 | 1,287 |
| Lauderdale County | 75 | Meridian | LD | 1833 | 80,261 | 704 | 1,823 |
| Lawrence County | 77 | Monticello | LW | 1814 | 12,929 | 431 | 1,116 |
| Leake County | 79 | Carthage | LK | 1833 | 23,805 | 583 | 1,510 |
| Lee County | 81 | Tupelo | LE | 1866 | 82,910 | 450 | 1,165 |
| Leflore County | 83 | Greenwood | LF | 1871 | 32,317 | 592 | 1,533 |
| Lincoln County | 85 | Brookhaven | LI | 1870 | 34,869 | 586 | 1,518 |
| Lowndes County | 87 | Columbus | LO | 1830 | 59,779 | 502 | 1,300 |
| Madison County | 89 | Canton | MD | 1828 | 95,203 | 719 | 1,862 |
| Marion County | 91 | Columbia | MA | 1811 | 27,088 | 542 | 1,404 |
| Marshall County | 93 | Holly Springs | MR | 1836 | 37,144 | 706 | 1,829 |
| Monroe County | 95 | Aberdeen | MO | 1821 | 36,989 | 764 | 1,979 |
| Montgomery County | 97 | Winona | MT | 1871 | 10,925 | 407 | 1,054 |
| Neshoba County | 99 | Philadelphia | NE | 1833 | 29,676 | 570 | 1,476 |
| Newton County | 101 | Decatur | NW | 1836 | 21,720 | 578 | 1,497 |
| Noxubee County | 103 | Macon | NO | 1833 | 11,545 | 695 | 1,800 |
| Oktibbeha County | 105 | Starkville | OK | 1833 | 47,671 | 458 | 1,186 |
| Panola County | 107 | Batesville, Sardis | PA | 1836 | 34,707 | 684 | 1,772 |
| Pearl River County | 109 | Poplarville | PR | 1890 | 55,834 | 812 | 2,103 |
| Perry County | 111 | New Augusta | PE | 1820 | 12,250 | 647 | 1,676 |
| Pike County | 113 | Magnolia | PI | 1815 | 40,404 | 409 | 1,059 |
| Pontotoc County | 115 | Pontotoc | PO | 1836 | 29,957 | 497 | 1,287 |
| Prentiss County | 117 | Booneville | PS | 1870 | 25,276 | 415 | 1,075 |
| Quitman County | 119 | Marks | QU | 1877 | 8,223 | 405 | 1,049 |
| Rankin County | 121 | Brandon | RA | 1828 | 141,617 | 775 | 2,007 |
| Scott County | 123 | Forest | SC | 1833 | 28,264 | 609 | 1,577 |
| Sharkey County | 125 | Rolling Fork | SH | 1876 | 4,916 | 428 | 1,109 |
| Simpson County | 127 | Mendenhall | SI | 1824 | 27,503 | 589 | 1,526 |
| Smith County | 129 | Raleigh | SM | 1833 | 16,491 | 636 | 1,647 |
| Stone County | 131 | Wiggins | ST | 1916 | 17,786 | 445 | 1,153 |
| Sunflower County | 133 | Indianola | SU | 1844 | 29,450 | 694 | 1,797 |
| Tallahatchie County | 135 | Charleston, Sumner | TL | 1833 | 15,378 | 644 | 1,668 |
| Tate County | 137 | Senatobia | TA | 1873 | 28,886 | 404 | 1,046 |
| Tippah County | 139 | Ripley | TI | 1836 | 22,232 | 458 | 1,186 |
| Tishomingo County | 141 | Iuka | TS | 1836 | 19,593 | 424 | 1,098 |
| Tunica County | 143 | Tunica | TU | 1836 | 10,778 | 455 | 1,178 |
| Union County | 145 | New Albany | UN | 1870 | 27,134 | 416 | 1,077 |
| Walthall County | 147 | Tylertown | WL | 1912 | 15,443 | 404 | 1,046 |
| Warren County | 149 | Vicksburg | WR | 1809 | 48,773 | 587 | 1,520 |
| Washington County | 151 | Greenville | WS | 1827 | 51,137 | 724 | 1,875 |
| Wayne County | 153 | Waynesboro | WA | 1809 | 20,747 | 810 | 2,098 |
| Webster County | 155 | Walthall | WE | 1874 | 10,253 | 423 | 1,096 |
| Wilkinson County | 157 | Woodville | WK | 1802 | 9,878 | 677 | 1,753 |
| Winston County | 159 | Louisville | WI | 1833 | 19,198 | 607 | 1,572 |
| Yalobusha County | 161 | Water Valley, Coffeeville | YA | 1833 | 12,678 | 467 | 1,210 |
| Yazoo County | 163 | Yazoo City | YZ | 1823 | 28,065 | 920 | 2,383 |
