- Population: 39,825 (Change since 1990: +13.0%)
- Created: November 13, 1857
- County seat: Rolla
- Largest town: Rolla (Pop. 16,367)
- Name origin: John F. Phelps
- Arlington (Unincorporated)
- Latitude & Longitude: 37°55'13" N, 91°58'15" W
- USGS Quad: Newburg
- Austria (Historical)
- Latitude & Longitude: 37°50'58" N, 91°33'17" W
- Survey: T. 36 N., R. 6 W., Sec. 11
- Elevation: 1140
- USGS Quad: Seaton
- Beulah (Unincorporated)
- Latitude & Longitude: 37°37'27" N, 91°55'01" W
- USGS Quad: Beulah
- Blooming Rose (Unincorporated)
- Latitude & Longitude: 37°36'46" N, 91°58'21" W
- USGS Quad: Beulah
- Clementine (Unincorporated)
- Latitude & Longitude: 37°52'35" N, 92°01'02" W
- USGS Quad: Dixon
- Clinton (Unincorporated)
- Latitude & Longitude: 37°48'49" N, 91°33'34" W
- Elevation: 1171
- USGS Quad: Seaton
- Craddock (Unincorporated)
- Latitude & Longitude: 37°38'22" N, 91°50'45" W
- USGS Quad: Edgar Springs
- De Camp (Historical)
- Latitude & Longitude: 37°53'60" N, 91°35'43" W
- Survey: T. 37 N., R. 6 W., Sec. 28
- Elevation: 900
- USGS Quad: Maramec Spring
- Dillon (Unincorporated)
- Located along CR 3120 between Rolla and St. James
- Latitude & Longitude: 37°58'19" N, 91°41'52" W
- USGS Quad: Dillon
- Doolittle (Fourth-class city)
- Population: 644 (Change since 1990: +7.5%)
- Located near the I-44 interchange with Route T between Jerome and Rolla
- Latitude & Longitude: 37°56'25" N, 91°52'51" W
- Duke (Unincorporated)
- Latitude & Longitude: 37°39'37" N, 92°00'38" W
- Elevation: 1115
- USGS Quad: Big Piney
- Edgar Springs (Fourth-class city)
- Population: 190 (Change since 1990: -11.6%)
- Latitude & Longitude: 37°42'16" N, 91°51'59" W
- Post office: Dec. 7, 1866 - Now
- Flag Spring (Unincorporated)
- Located on Route B just northeast of St. James
- Latitude & Longitude: 38°01'30" N, 91°36'13" W
- USGS Quad: Rosati
- Flat (Unincorporated)
- Latitude & Longitude: 37°44'43" N, 91°55'44" W
- USGS Quad: Flat
- Jerome (Unincorporated)
- Latitude & Longitude: 37°55'34" N, 91°58'39" W
- USGS Quad: Newburg
- Meramec Springs (Historical)
- Latitude & Longitude: 37°57'19" N, 91°32'05" W
- Survey: T. 37 N., R. 6 W., Sec. 1
- Elevation: 803
- USGS Quad: Maramec Spring
- Newburg (Fourth-class city)
- Population: 484 (Change since 1990: -17.8%)
- Located near the junction of Route T and Route P southwest of Doolittle
- Latitude & Longitude: 37°54'51" N, 91°54'09" W
- Northwye (Unincorporated)
- Latitude & Longitude: 37°58'30" N, 91°45'20" W
- USGS Quad: Rolla
- Powellville (Unincorporated)
- Latitude & Longitude: 37°53'22" N, 92°00'52" W
- USGS Quad: Dixon
- Rolla (Third-class city)
- Population: 16,367 (Change since 1990: +16.2%)
- Latitude & Longitude: 37°57'05" N, 91°46'16" W
- Rosati (Unincorporated)
- Latitude & Longitude: 38°01'37" N, 91°31'51" W
- Elevation: 1077
- USGS Quad: Rosati
- Royal (Unincorporated)
- Located on Route B south of the bridge over Bourbeuse River
- Latitude & Longitude: 38°07'41" N, 91°34'47" W
- Elevation: 960
- USGS Quad: Redbird
- Schundler (Unincorporated)
- Latitude & Longitude: 38°00'23" N, 91°35'47" W
- USGS Quad: Rosati
- Seaton (Unincorporated)
- Located near the end of Route JJ southeast of Rolla
- Latitude & Longitude: 37°48'28" N, 91°36'08" W
- USGS Quad: Seaton
- Signal (Historical)
- Latitude & Longitude: 38°01'52" N, 91°48'55" W
- Survey: T. 38 N., R. 8 W., Sec. 9
- Elevation: 900
- USGS Quad: Vichy
- Spring Creek (Unincorporated)
- Located on Route J at the Pulaski County line
- Latitude & Longitude: 37°45'45" N, 92°01'26" W
- USGS Quad: Devils Elbow
- St. James (Third-class city)
- Population: 3,704 (Change since 1990: +13.8%)
- Latitude & Longitude: 37°59'50" N, 91°36'51" W
- Sugartree (Unincorporated)
- Latitude & Longitude: 37°58'04" N, 91°58'14" W
- USGS Quad: Newburg
- Vida (Unincorporated)
- Located at the junction of US 63 and Route W south of Rolla
- Latitude & Longitude: 37°51'25" N, 91°47'58" W
- Elevation: 1046
- USGS Quad: Yancy Mills
- Westcott (Historical)
- Latitude & Longitude: 37°58'19" N, 91°53'54" W
- Survey: T. 38 N., R. 9 W., Sec. 34
- Elevation: 950
- USGS Quad: Newburg
- Winkler (Unincorporated)
- Located on MO 68 in the southeast corner of the county
- Latitude & Longitude: 37°50'09" N, 91°33'25" W
- USGS Quad: Seaton
Name origin
Named for John Phelps, congressman and governor of Missouri
| Year | Population | Percent change |
|---|
| 1860 | 5,714 | -- |
| 1870 | 10,506 | +83.9% |
| 1880 | 12,568 | +19.6% |
| 1890 | 12,636 | +0.5% |
| 1900 | 14,194 | +12.3% |
| 1910 | 15,796 | +11.3% |
| 1920 | 14,941 | -5.4% |
| 1930 | 15,308 | +2.5% |
| 1940 | 17,437 | +13.9% |
| 1950 | 21,504 | +23.3% |
| 1960 | 25,396 | +18.1% |
| 1970 | 29,481 | +16.1% |
| 1980 | 33,633 | +14.1% |
| 1990 | 35,248 | +4.8% |
| 2000 | 39,825 | +13.0% |