Lyon County comprises 453,072 acres (721 sq miles) of land in southwestern Minnesota, 86% of which is farmland.
The county contains 20 townships and 11 incorporated cities. The City of Marshall is the county seat.
2000 Census
| | People | Households | Families | Housing Units |
| County | |
| Lyon | 25,425 | 9,715 | 6,334 | 10,298 |
| Cities | |
| Balaton | 637 | 276 | 186 | 296 |
| Cottonwood | 1,148 | 452 | 319 | 481 |
| Florence | 61 | 21 | 17 | 27 |
| Garvin | 159 | 57 | 44 | 68 |
| Ghent | 315 | 128 | 89 | 131 |
| Lynd | 346 | 130 | 80 | 134 |
| Marshall | 12,735 | 4,914 | 2,914 | 5,182 |
| Minneota | 1,449 | 590 | 389 | 614 |
| Russell | 371 | 157 | 105 | 170 |
| Taunton | 207 | 72 | 39 | 77 |
| Tracy | 2,268 | 922 | 533 | 1,013 |
| Townships | |
| Amiret | 230 | 85 | 71 | 95 |
| Clifton | | | | |
| Coon Creek | | | | |
| Custer | | | | |
| Eidsvold | | | | |
| Fairview | | | | |
| Grandview | | | | |
| Island Lake | | | | |
| Lake Marshall | | | | |
| Lucas | | | | |
| Lynd | | | | |
| Lyons | | | | |
| Monroe | | | | |
| Nordland | | | | |
| Rock Lake | | | | |
| Shelburne | | | | |
| Sodus | | | | |
| Stanley | | | | |
| Vallers | | | | |
| Westerheim | 286 | 97 | 78 | 100 |
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