Rock Island County, Illinois

Rock Island County is a county in Illinois, United States, on the Mississippi River across from
Davenport and Bettendorf, Iowa. It had a population of 144,672 at the 2020 census, an estimated
142,757 by 2024, and covers 428 square miles (1,110 km2) of land centred near 41°28′N 90°34′W.

Rock Island is the county seat; its postal code is 61201. The county holds 4 cities, 11
incorporated villages and 9 unincorporated communities across 18 townships, and it runs on Central
Time.

Towns & Villages in Rock Island County

Rock Island County has 24 named places on record: 4 cities, 11 incorporated villages and 9
census-designated places (CDPs) with no local government of their own. CDP stands for census
designated place; Unincorp. covers crossroads and rural communities with no formal boundary.

Rock Island Arsenal is both a place name and the federal property it sits on — a 946-acre
island in the Mississippi River that carries no township assignment because it is entirely
government land, not part of any civil township. Rapids City shares Port Byron’s 61275 ZIP
code rather than having its own; the two villages sit about two miles apart along the river.

Townships

The Census Bureau has not published 2020 population figures broken out by Rock Island
County’s 18 civil townships; the most recent official township-level counts are from the 2010
census. They are listed below by that 2010 population, descending, with each township’s main
settlement.

ZIP Codes

• 61201 — Rock Island (the county seat, also serves 61204 and 61299 as PO box ZIPs)
• 61265 — Moline (also serves 61266, a Moline PO box ZIP)
• 61244 — East Moline
• 61282 — Silvis
• 61264 — Milan
• 61240 — Coal Valley
• 61239 — Carbon Cliff
• 61256 — Hampton
• 61275 — Port Byron (also serves Rapids City)
• 61232 — Andalusia
• 61242 — Cordova
• 61279 — Reynolds
• 61257 — Hillsdale

Coyne Center, Oak Grove, Edgington, Campbell’s Island, Rock Island Arsenal, Illinois City,
Taylor Ridge, Barstow, Joslin and Buffalo Prairie have no ZIP code of their own; mail there is
delivered under the nearest incorporated town’s code.

Geography

Rock Island County sits on the north-western edge of Illinois, bounded by the Mississippi River
on its north and west sides. Of its 451 square miles total, 428 are land and 24 are water, about
5.2 percent — higher than most inland Illinois counties, since the county’s entire
northern and western border runs along the Mississippi. The Rock River, whose Sauk name
Sinnissippi means “rocky waters,” enters the Mississippi near the county’s
namesake island, now called Arsenal Island.

Across the Mississippi to the north lies Clinton County, Iowa, and to the northwest Scott
County, Iowa. Whiteside County, Illinois borders to the northeast, Henry County, Illinois to the
southeast, and Mercer County, Illinois to the south. Louisa County, Iowa and Muscatine County,
Iowa lie across the river to the southwest and west. Clinton County, Scott County, Whiteside County, Henry County, Louisa County and Muscatine County all border Rock Island
directly; Mercer County has no live page on this site to link to.

Demographics

Rock Island County had a population of 144,672 at the 2020 census, and the latest estimate puts
the county near 142,757 residents in 2024, a slight decline. Moline and Rock Island are by far the
two largest communities, together holding well over a third of the county’s population.
Median household income runs $67,159 (2024 ACS estimate), well below Illinois’s statewide
figure of $80,306 (2023 ACS). Population density works out to roughly 338 people per square mile
of land, reflecting the county’s position inside the Davenport-Moline-Rock Island, IA-IL
metropolitan area, one of four Illinois and Iowa counties that make it up.

Economy & Local Life

Manufacturing employs the most workers in the county, about 10,293 people, followed by health
care and social assistance at 9,212 and retail trade at 7,777. Deere & Company, the world’s
largest agricultural machinery manufacturer, is headquartered in Moline and lists roughly 2,775
employees at that campus alone. Rock Island Arsenal, on the island the county is named for,
employs about 6,000 people and is described as the largest government-owned weapons
manufacturing arsenal in the United States; it has produced military equipment for the Army since
the 1880s and is a National Historic Landmark. Quad City International Airport, based in Moline,
anchors regional air service and its own cluster of aviation jobs. Augustana College, a private
liberal-arts college founded in 1860, has been based in Rock Island since 1875 and is a major
local employer and institution in its own right.

History

Illinois organized Rock Island County in 1831, carving it out of Jo Daviess County. It takes
its name from Rock Island, an island in the Mississippi River that is now called Arsenal Island.
The U.S. Army established Rock Island Arsenal on that island in 1862, and the site has
manufactured ordnance and military equipment for the Army since the 1880s; it is now a National
Historic Landmark.

Passenger rail once linked the county directly to Chicago: the Rock Island Railroad’s
Quad Cities Rocket served Moline until it stopped running in 1979. A new Amtrak station was built
in Moline as part of a long-planned Chicago-to-Quad-Cities route, but as of this writing the line
has not opened and no train service currently operates from it, after more than a decade of
construction and disputes between state transportation agencies and the freight railroad that
owns the tracks.

Getting There

Interstates 74, 80, 88 and 280 all cross the county, along with US 6, US 67 and US 150, and
Illinois Routes 5, 84, 92, 94, 110 and 192.

• Davenport, Iowa — directly across the Mississippi from Rock Island
• Galesburg — about 45 miles southeast
• Peoria — about 85 miles southeast
• Iowa City, Iowa — about 55 miles west

Quad City International Airport, in Moline, is the county’s own commercial airport,
offering scheduled flights without requiring a drive to another metro area. Quad Cities
MetroLINK provides local bus transit across Moline, Rock Island, East Moline and Silvis. There is
currently no operating Amtrak service to the county; the built-but-unused Moline station is
covered under History above.

Frequently Asked Questions

Where is Rock Island County located?
It sits on the Mississippi River in north-western Illinois, directly across from Davenport and
Bettendorf, Iowa, part of the Quad Cities metro area.

What is the population of Rock Island County?
144,672 at the 2020 census, with a 2024 estimate near 142,757.

How big is Rock Island County?
451 square miles (1,170 km2) total, of which 428 square miles are land and 24 square miles are
Mississippi River water.

What is the county seat of Rock Island County?
Rock Island, home to Augustana College and postal code 61201.

How many towns and cities are in Rock Island County?
Four cities — Moline, Rock Island, East Moline and Silvis — plus 11 incorporated
villages and 9 unincorporated census-designated places.

What ZIP codes does Rock Island County use?
61201 and 61204 for Rock Island, 61265 and 61266 for Moline, 61244 for East Moline, 61282 for
Silvis, and separate codes for each of the county’s larger villages, listed above.

What is Rock Island County known for?
Rock Island Arsenal, the largest government-owned weapons manufacturing arsenal in the country,
and Deere & Company’s world headquarters in Moline.

More counties in this state: Towns and villages in Illinois.