Mark Costello
Iowa State Senator, District 8 since 2016. Next on the ballot in 2028.
- In office
- 9 yrs
- Since 2016
- Bills became law
- 0
- 10 sponsored, 2025–2026 session
- Votes missed
- 0.3%
- Chamber median 2.9%
- With party
- 99%
- On votes splitting the parties
- Last margin
- +41.2
- Won 2024
- Next election
- 2028
- Nov 7, 2028
Source: Wikidata, congress-legislators and Open States; 99chambers legislative recordsUpdated Oct 27, 2026, 9:43 AM ET
Committees
As of 2026-10.
- Health and Human Services · vice chair
- Agriculture
- Appropriations
- Health Policy Oversight
- Natural Resources and Environment
- Subacute Mental Health Care Services Interim Study
- Transportation
- Veterans Affairs
Source: Open States committeesUpdated Oct 27, 2026, 9:43 AM ET
Legislation
bicycling · Failed in the Senate Mar 2025
deer · Failed in the Senate Feb 2025
appropriations · Failed in committee Mar 2025
attorney general · Failed in committee Mar 2025
controlled substances · Failed in committee Feb 2025
Source: Open States billsUpdated Nov 6, 2026, 4:22 PM ET
Voting record
Where Costello sits in the Iowa State Senate
Costello is closer to the center than 30% of the chamber's Republicans.
Closest: Tim Kraayenbrink, Jason Schultz, Carrie Koelker
Source: 99chambers roll-call scalingUpdated Nov 6, 2026, 4:49 PM ET
With Costello’s party
- Votes with the chamber's Republicans99%
Black tick: the average of Republicans in the Iowa State Senate.
Source: 99chambers legislative scores from roll calls and cosponsorships
Key votes
Votes chosen for their effect, not their side: Costello’s vote, each party’s majority, and the result. An orange vote differs from most Republicans.
| Date | Bill | Costello | Rep. majority | Dem. majority | Result |
|---|---|---|---|---|---|
| Oct 2, 2026 | HF 2801: A bill for an act modifying the major economic growth attraction program, and including… | Yes | Yes | No | Passed 28–19 |
| May 2, 2026 | HF 2770: A bill for an act relating to and making appropriations to the justice system, providing… | Yes | Yes | No | Passed 29–17 |
| May 2, 2026 | HF 2787: A bill for an act prohibiting warrant resolution clinics, including enforcement… | Yes | Yes | No | Passed 31–12 |
| May 2, 2026 | SF 2490: A bill for an act relating to oil and gas production, including filing requirements, the… | Yes | Yes | No | Passed 35–11 |
| May 2, 2026 | HF 2781: A bill for an act relating to allocations of moneys from the juvenile detention home fund. | Yes | Yes | No | Passed 34–9 |
Source: 99chambers key votes from Congress.gov, Voteview and Open States roll calls
Career
Offices held, and every time Costello was on a ballot. Filled marks are general elections won; hollow marks are primaries; an orange outline is a loss.
Source: 99chambers results archive (MEDSL, Klarner, state election offices)
Elections
Margin against the seat’s presidential baseline: how the seat voted for president in the same or nearest year.
| Year | Race | Result | Margin |
|---|---|---|---|
| 2024 | Iowa State Senate, District 8 | Won | R+41.2 |
| 2020 | Iowa State Senate, District 12 | Won | R+38.3 |
| 2016 | Iowa State Senate, District 12 | Won | R+56.7 |
| 2014 | Iowa House of Representatives, District 23 | Won | — |
| 2012 | Iowa House of Representatives, District 23 | Won | — |
Source: 99chambers results archive
Seats Costello has held
- Iowa State Senate, District 8 · since 2024
- Iowa State Senate, District 12 · since 2016
- Iowa House of Representatives, District 23 · 2012–2016
Source: 99chambers results archive
Who Costello has run against
- Ryan Lee Roenfeld (D) · 2024 general, won
- Joseph Norris (D) · 2020 general, won
- Don W. Brantz (L) · 2016 general, won
Source: 99chambers results archive
How we know Costello
One person, matched across every source we use.
- Open States ocd-person/37b1879c-5435-4c28-bb62-fa71fbabbbdb
Source: Identity links: Wikidata, congress-legislators, Open States, FECUpdated Oct 27, 2026, 9:43 AM ET