Kelso was originally called Spring Hill, until 1858 when the post office changed names to prevent conflicts with other Spring Hills in Missouri. One source says that the town may also have been called Pikeston, Vollmersville, and Dannenmullersville at one time or another.
| Year | Population | Percent change |
|---|---|---|
| 1910 | 190 | -- |
| 1920 | 228 | +20.0% |
| 1930 | 221 | -3.1% |
| 1940 | 223 | +0.9% |
| 1950 | 276 | +23.8% |
| 1960 | 258 | -6.5% |
| 1970 | 401 | +55.4% |
| 1980 | 455 | +13.5% |
| 1990 | 526 | +15.6% |
| 2000 | 527 | +0.2% |