- Population: 18,293 (Change since 1990: +3.8%)
- Created: January 2, 1818
- County seat: Jonesboro
- Largest town: Anna (Pop. 5,136)
- Highest point: Bald Knob, 1025 ft.
- Name origin: Federal union
- Aldridge (Unincorporated)
- Located on IL 3 just south of the crossing over Big Muddy River
- Latitude & Longitude: 37°33'30" N, 89°28'12" W
- Survey: T. 11 S., R. 3 W., Sec. 17
- Elevation: 351
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- Maps: 1897 Galbraith (Shown south of Ware) and 1898
- Alto Pass (Village)
- Population: 388 (Change since 1990: -7.0%)
- Located on IL 127 northwest of Cobden
- Latitude & Longitude: 37°34'13" N, 89°19'03" W
- Founded: Jan. 20, 1875
- Anna (City)
- Population: 5,136 (Change since 1990: +6.9%)
- Located adjacent to Jonesboro at the intersection US 51 and IL 146
- Latitude & Longitude: 37°27'37" N, 89°14'49" W
- Name origin: Anna Davie
- Founded: 1853 by Winstead Davie
- Post office: Mar. 14, 1855 - Now (but called Jonesboro Station
Feb. 7, 1857 - Mar. 11, 1857)
- Balcom (Unincorporated)
- Located just off US 51 between Anna and Dongola
- Latitude & Longitude: 37°24'47" N, 89°12'22" W
- Survey: T. 13 S., R. 1 W., Sec. 3
- Elevation: 496
- Precinct: Balcom
- USGS Quad: Anna
- Bennett Landing (Historical)
- Located along the Mississippi River northeast of Neelys Landing, MO
- Latitude & Longitude: 37°32'02" N, 89°29'54" W
- Survey: T. 11 S., R. 4 W., Sec. 25
- Elevation: 340
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- Berryville (Unincorporated)
- Located west of Jonesboro
- Latitude & Longitude: 37°27'25" N, 89°17'16" W
- Survey: T. 12 S., R. 2 W., Sec. 23
- Elevation: 460
- Precinct: Jonesboro District No. 2
- USGS Quad: Jonesboro
- Bradshaw (Historical)
- Cobden (Village)
- Population: 1,116 (Change since 1990: +2.4%)
- Located on the railroad north of Anna
- Latitude & Longitude: 37°31'53" N, 89°15'12" W
- Name origin: Sir Richard Cobden
- Founded: 1857 as South Pass
- Dongola (Village)
- Population: 806 (Change since 1990: +10.7%)
- Located just west of I-57 Exit 24 southeast of Anna
- Latitude & Longitude: 37°21'40" N, 89°09'57" W
- Founded: May 23, 1857 by Ebeni Leavenworth
- Post office: Nov. 9, 1855 - Apr. 16, 1857 (Unionville); Apr. 16, 1857 - Now (Dongola)
- Dutch Mills (Unincorporated)
- Located on IL 127 south of Jonesboro
- Latitude & Longitude: 37°24'55" N, 89°16'22" W
- Survey: T. 13 S., R. 2 W., Sec. 1
- Elevation: 440
- Precinct: Jonesboro District No. 2
- USGS Quad: Jonesboro
- Halsey (Unincorporated)
- Located on the railroad north of La Rue, near the bridge
over Big Muddy River
- Latitude & Longitude: 37°34'02" N, 89°27'10" W
- Survey: T. 11 S., R. 3 W., Sec. 16-17
- Elevation: 352
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- Hamburg Landing (Unincorporated)
- Located near the Mississippi River opposite Bainbridge, MO
- Latitude & Longitude: 37°24'23" N, 89°24'44" W
- Precinct: Union District No. 1
- USGS Quad: Ware
- Maps: 1818 and 1833 (Hamburg)
- Jonesboro (City)
- Population: 1,853 (Change since 1990: +7.2%)
- Located at intersection IL 127 and IL 146 west of Anna
- Latitude & Longitude: 37°27'06" N, 89°16'05" W
- Kaolin (Unincorporated)
- Located southwest of Cobden
- Latitude & Longitude: 37°30'42" N, 89°17'60" W
- Survey: T. 11 S., R. 2 W., Sec. 35
- Elevation: 480
- Precinct: Cobden District No. 2
- USGS Quad: Cobden
- Kings Ferry (Historical)
- Located along the Big Muddy River north of La Rue
- Latitude & Longitude: 37°35'54" N, 89°26'52" W
- Survey: T. 11 S., R. 3 W., Sec. 4
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- La Rue (Unincorporated)
- Located on the railroad north of Wolf Lake
- Latitude & Longitude: 37°32'44" N, 89°27'13" W
- Survey: T. 11 S., R. 3 W., Sec. 20
- Elevation: 354
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- Lick Creek (Unincorporated)
- Alternate name: Lickcreek
- Located just off I-57 northeast of Anna
- Latitude & Longitude: 37°31'21" N, 89°04'30" W
- Survey: T. 11 S., R. 1 E., Sec. 35
- Elevation: 500
- Precinct: Lick Creek
- USGS Quad: Lick Creek
- Maps: 1876 atlas and 1878 (Lick)
- Mason (Unincorporated)
- Latitude & Longitude: 37°31'25" N, 89°15'15" W
- Elevation: 600
- Precinct: Cobden District No. 1
- USGS Quad: Cobden (Not shown)
- Mile 32 (Historical)
- Mill Creek (Village)
- Population: 76 (Change since 1990: -12.6%)
- Located on IL 127 south of Springville, near the Alexander County line
- Latitude & Longitude: 37°20'30" N, 89°15'09" W
- Moscow (Unincorporated)
- Located between Balcom and Vienna
- Latitude & Longitude: 37°24'41" N, 89°03'09" W
- Survey: T. 13 N., R. 1 E., Sec. 1
- Elevation: 425
- Precinct: Stokes
- USGS Quad: Mount Pleasant
- Maps: 1876 atlas, 1878, and 1895 McNally
- Mount Pleasant (Unincorporated)
- Located just off IL 146 between Anna and Vienna
- Latitude & Longitude: 37°27'07" N, 89°04'25" W
- Survey: T. 12 S., R. 1 E., Sec. 23
- Elevation: 494
- Precinct: Stokes
- USGS Quad: Mount Pleasant
- Founded: 1858 by Caleb Musgrave
- Post office: Sept. 5, 1825 - May 15, 1909
- Map: 1876 atlas
- Mountain Glen (Unincorporated)
- Located just west of Cobden
- Latitude & Longitude: 37°31'39" N, 89°17'23" W
- Survey: T. 11 S., R. 2 W., Sec. 26
- Elevation: 455
- Precinct: Cobden District No. 2
- USGS Quad: Cobden
- Map: 1898
- Pottsville (Historical)
- Located southeast of Ware in the Union County Conservation Area
- Latitude & Longitude: 37°25'19" N, 89°21'27" W
- Survey: T. 12 S., R. 2 W., Sec. 32
- Elevation: 342
- Precinct: Jonesboro District No. 2
- USGS Quad: Jonesboro
- Progress (Historical)
- Located northeast Cobden and south of Little Grassy Lake
- Latitude & Longitude: 37°35'12" N, 89°07'29" W
- Survey: T. 11 S., R. 1 E.
- Precinct: Saratoga
- USGS Quad: Lick Creek (Not shown)
- Maps: 1895 McNally and 1897 Galbraith
- Reynoldsville (Unincorporated)
- Located along IL 3/IL 146 south of Ware
- Latitude & Longitude: 37°22'02" N, 89°23'42" W
- Survey: T. 13 S., R. 3 W., Sec. 24
- Elevation: 342
- Precinct: Union District No. 1
- USGS Quad: McClure
- Map: 1898 (Reynolds)
- Saratoga (Unincorporated)
- Previously known as: Western Saratoga
- Located northeast of Anna
- Latitude & Longitude: 37°30'32" N, 89°09'25" W
- Survey: T. 12 S., R. 1 W., Sec. 1
- Elevation: 435
- Precinct: Saratoga
- USGS Quad: Makanda
- Maps: 1876 atlas (Western Saratoga) and 1897 Galbraith (Western Saratoga)
- Springville (Unincorporated)
- Located along IL 127 between Dutch Mills and Mill Creek
south of Jonesboro
- Latitude & Longitude: 37°22'28" N, 89°16'03" W
- Survey: T. 13 S., R. 1 W., Sec. 19
- Elevation: 440
- Precinct: Mill Creek
- USGS Quad: Mill Creek
- Maps: 1876 atlas and 1898
- The Hall (Unincorporated)
- Latitude & Longitude: 37°31'24" N, 89°05'53" W
- Elevation: 569
- Precinct: Lick Creek
- USGS Quad: Lick Creek (Not shown)
- Union Point (Unincorporated)
- Previously known as: Preston
- Located along the Mississippi River, south of the mouth
of Big Muddy River
- Latitude & Longitude: 37°32'57" N, 89°30'14" W
- Elevation: 350
- Precinct: Union District No. 2
- USGS Quad: Neelys Landing (Not shown)
- Maps: 1875 Asher, 1876 atlas (Preston or Union Point P.O), and 1883 Tenney (Union Pt P.O. or Preston)
- Valley Mission (Unincorporated)
- Located east of Reynoldsville
- Latitude & Longitude: 37°21'29" N, 89°20'21" W
- Survey: T. 13 S., R. 2 W., Sec. 28
- Elevation: 390
- Precinct: Union District No. 1
- USGS Quad: Mill Creek
- Ware (Unincorporated)
- Located at northern intersection of IL 3 and IL 146 west of Jonesboro
- Latitude & Longitude: 37°26'52" N, 89°23'38" W
- Survey: T. 12 S., R. 3 W., Sec. 25
- Elevation: 347
- Precinct: Union District No. 1
- USGS Quad: Ware
- Water Valley (Unincorporated)
- Located northeast of Cobden
- Latitude & Longitude: 37°33'31" N, 89°10'31" W
- Survey: T. 11 S., R. 1 W., Sec. 14
- Elevation: 570
- Precinct: Cobden District No. 1
- USGS Quad: Makanda
- Wayside (Unincorporated)
- Previously known as: Oakville
- Located in the northeast corner of the county, west of Goreville
- Latitude & Longitude: 37°34'15" N, 89°04'33" W
- Survey: T. 11 S., R. 1 E., Sec. 11
- Precinct: Lick Creek
- USGS Quad: Lick Creek
- Post office: Nov. 6, 1885 - Jun. 8, 1906 (Oakville); Jun. 8, 1906 - Sept. 29, 1917 (Wayside)
- Willard Landing (Historical)
- Previously known as: Willards, Greens Ferry, , and Big Barn
- Located on the Mississippi River west of Jonesboro
and opposite Moccasin Springs, MO
- Latitude & Longitude: 37°27'19" N, 89°27'03" W
- Precinct: Union District No. 1
- USGS Quad: Ware
- Maps: 1876 atlas (Willard's Landing P.O. or Greens Ferry) and 1878
- Wolf Lake (Unincorporated)
- Located along IL 3 northwest of Ware
- Latitude & Longitude: 37°30'15" N, 89°26'18" W
- Survey: T. 12 S., R. 3 W., Sec. 20
- Elevation: 353
- Precinct: Union District No. 2
- USGS Quad: Wolf Lake
- Post office: May 17, 1890 - Now
Name origin
Named for the Federal union of the United States
| Year | Population | Percent change |
|---|
| 1820 | 2,362 | -- |
| 1830 | 3,239 | +37.1% |
| 1840 | 5,524 | +70.5% |
| 1850 | 7,615 | +37.9% |
| 1860 | 11,172 | +46.7% |
| 1870 | 16,518 | +47.9% |
| 1880 | 18,102 | +9.6% |
| 1890 | 21,549 | +19.0% |
| 1900 | 22,610 | +4.9% |
| 1910 | 21,856 | -3.3% |
| 1920 | 20,249 | -7.4% |
| 1930 | 19,883 | -1.8% |
| 1940 | 21,528 | +8.3% |
| 1950 | 20,500 | -4.8% |
| 1960 | 17,645 | -13.9% |
| 1970 | 16,071 | -8.9% |
| 1980 | 17,765 | +10.5% |
| 1990 | 17,619 | -0.8% |
| 2000 | 18,293 | +3.8% |