Iowa State Senate seat · lines in effect since 2022
Iowa Senate District 8
A district of about 70,000 people, 29% of adults with a bachelor's degree. It votes R+38.7 relative to the nation for president.
2024 election
Nov 5, 2024- Mark Costello (R) · won70.5%
- Ryan Lee Roenfeld (D)29.3%
Source: MIT Election Data and Science LabUpdated Sep 30, 2026, 12:13 PM ET
Where it sits among all 50 seats
Every Iowa State Senate seat by partisan lean, from most Democratic to most Republican. Lean is the seat's presidential vote on current lines, relative to the nation.
Democratic
Source: 99chambers: 2024 and 2020 presidential results on current lines, relative to the nation (2024 weighted 3:1)Updated Oct 16, 2026, 5:19 AM ET
Every election for this seat
15 races since 1972; the seat changed party 4 times. District numbers are redrawn after each census: each group is one set of lines.
| Year | Winner | Runner-up | Won by |
|---|---|---|---|
| Lines first used in 2022 | |||
| 2024 | Mark Costello (R) | Ryan Lee Roenfeld (D) | 41.1 |
| Lines first used in 2012 | |||
| 2020 | Dan Dawson (R) | Steve Gorman (D) | 4.4 |
| 2016 | Dan Dawson (R)Flip | Michael E. Gronstal (D) | 8.1 |
| 2012 | Michael E. Gronstal (D) | Al Ringgenberg (R) | 10.6 |
| Lines first used in 2002 | |||
| 2008 | Mary Jo Wilhelm (D)Flip | Mark Zieman (R) | 3.6 |
| 2004 | Mark Zieman (R) | John Beard (D) | 10.9 |
| 2002 | Mark Zieman (R) | Lyle Otte (D) | 13.3 |
| Lines first used in 1992 | |||
| 2000 | E. Thurman Gaskill (R) | William S. Farnham (D) | 13.7 |
| 1996 | James Edward Black (R)Flip | Berl E. Priebe (D) | 6.5 |
| 1992 | Berl E. Priebe (D) | Larry E. Miller (R) | 1.2 |
| Lines first used in 1982 | |||
| 1988 | Berl E. Priebe (D) | David J. Hanson (R) | 37.5 |
| 1984 | Berl E. Priebe (D) | — | Unopposed |
| Lines first used in 1972 | |||
| 1980 | Rolf V. Craft (R) | — | Unopposed |
| 1976 | Rolf V. Craft (R)Flip | Richard R. Nelson (D) | 13.3 |
| 1972 | H. L. Heying (D) | George L. Shawver (R) | 0.7 |
Won by: the winner's lead over the runner-up, in points of the vote. Source: 99chambers results archive (MEDSL, Klarner, state election offices)
Districts that overlap District 8
The state's districts in other chambers that share residents with this one, and the share of District 8's area in each.
- U.S. House
- IA-4 100%
Every race on these lines
Results recomputed from precinct returns as if today's boundaries had always existed, so years compare like for like.
| 2024 | |
|---|---|
| President | R+37.8 |
Outlined: the race for this seat itselfBlank: no race that year
Source: 99chambers results archive: precinct results allocated to current lines; 2026: civicAPIUpdated Nov 8, 2026, 7:01 PM ET
Who lives here, compared
Grey bars show the spread of all 50 seats. Small marks are other seats in Iowa. The black marker is District 8.
Higher than 57% of seats.
Higher than 67% of seats.
Lower than 86% of seats.
Lower than 71% of seats.
Lowest of 50 seats.
Less dense than 86% of seats.
Source: Census Bureau, American Community Survey 2020–2024 5-year estimates, allocated to current linesUpdated Oct 13, 2026, 5:06 AM ET
Seats most like this one
Nearest seats on demographics, density and lean.
District 525% college gradsR+40.2Held RDistrict 19
25% college gradsR+34.6Held RDistrict 29
26% college gradsR+29.4Held RDistrict 9
21% college gradsR+42.5Held R
Source: Census Bureau, American Community Survey 2020–2024 5-year estimates, allocated to current lines; 99chambers: 2024 and 2020 presidential results on current lines, relative to the nation (2024 weighted 3:1)Updated Oct 16, 2026, 5:19 AM ET