16th Annual Rock CF Rivers Half Marathon banner
16th Annual Rock CF Rivers Half Marathon logo

16th Annual Rock CF Rivers Half Marathon 2027

Date
Sunday, March 21, 2027
Start time
8:00 AM start (Detroit)
Entry fee
From $40
Included with entry
Includes a shirt
Fundraising
Takes optional donations when you register
Register on RunSignup

Registration is open.

We earn a small commission when you register through this link, at no cost to you. Details

Official race website

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Events and entry fees

EventDistanceWhenEntry feeCap
15K15KMar 21, 20278:00 AM$75300
Half MarathonHalf MarathonMar 21, 20278:00 AM$90800
5K Run/Walk5KMar 21, 20278:15 AM$40500
Virtual RunVirtual–Mar 21, 20278:00 AM$50150

Entry fees exclude processing fees. Prices and dates come from the race's registration page and refresh nightly.

Race day planning

Entry fee schedule

  • 15K: $75 until Mar 21.
  • Half Marathon: $90 until Mar 21.
  • 5K Run/Walk: $40 until Mar 21.

Online registration closes Mar 21, 2027, unless the race fills first.

How the price compares

At $90, entry is about 33 percent above a typical half marathon in Michigan, which costs $67.50 right now.

What a typical finish looks like

A typical finisher at a half marathon in Michigan runs 2:07:11, about 9:42 a mile, based on 72 races with published results. Women typically finish in 2:14:18 and men in 1:58:17.

Light and altitude

Sunrise on race morning is at about 7:36 AM, and the 15K starts at 8:00 AM. The start sits about 610 feet above sea level.

Fees exclude processing fees. Comparisons use current entry fees and published results from races nearby.

Start location and course

7800 Grays Dr, Grosse Ile, MI 48138

The pin marks the address the race lists, which is usually the start. The organizers have not shared a course map with us yet.

Half Marathon

675
finishers
1:57:09
median (8:56 /mi)
1:03:19
winning time
49% / 51%
women / men
median 1:57:091:15:493:09:30
Finish times, fastest to slowest. Each bar is a slice of the field; the dashed line is the median.

5K Run/Walk

399
finishers
35:35
median (11:29 /mi)
17:24
winning time
59% / 41%
women / men

15K

186
finishers
1:36:48
median (10:23 /mi)
54:18
winning time
67% / 33%
women / men

Aggregated from official results (Michigan Running Foundation) for 16th Annual Rock CF Rivers Half Marathon. Individual finisher names are not stored here.

How fast do you need to be at 16th Annual Rock CF Rivers Half Marathon?

At the 2026 Half Marathon, the fastest tenth finished in 1:29:35 or better, the top quarter in 1:41:43, and half the field in 1:57:09; the last tenth came in after 2:39:02.

At the 2026 5K Run/Walk, the fastest tenth finished in 24:47 or better, the top quarter in 29:35, and half the field in 35:35; the last tenth came in after 57:10.

At the 2026 15K, the fastest tenth finished in 1:11:44 or better, the top quarter in 1:22:31, and half the field in 1:36:48; the last tenth came in after 2:00:00.

Third place by age group, 2026 Half Marathon
AgeWomenMen
Under 201:50:571:29:02
20-291:27:061:15:49
30-391:26:061:10:55
40-491:32:411:23:01
50-591:38:581:28:28
60-691:54:021:39:59

Groups with fewer than five finishers are left out. Awards vary by race; check the race's rules.

What would my time get me?

Where a finish time would have placed in 2026.

Finishers by year

Up 15 percent since 2025.

All events combined, from official results.

16th Annual Rock CF Rivers Half Marathon Half Marathon year by year

From 2025 to 2026, the field went from 709 to 675 finishers, and the median time dropped from 1:58:10 to 1:57:09.

YearFinishersMedianFastest tenthWinner
2026675 (-5%)1:57:09under 1:29:351:03:19
20257091:58:10under 1:30:321:05:54

From each year's official results for the Half Marathon; virtual options are left out.

How fast is it?

Faster than most Michigan half marathons

The fastest quarter of the 2026 half marathon field finished under 1:41:43, against 1:52:52 in a typical Michigan half marathon, so times here run 10 percent faster.

  • 5K: Slower than most Michigan 5Ks. The fastest quarter of the 2026 5K field finished under 29:35, against 28:36 in a typical Michigan 5K, so times here run 3 percent slower.
  • 15K: Slower than most Michigan 15Ks. The fastest quarter of the 2026 15K field finished under 1:22:31, against 1:18:54 in a typical Michigan 15K, so times here run 5 percent slower.

Compares the fastest quarter of each field, so walkers and first-timers do not skew it. It reflects the course and the field together: a flat course, cool weather, or a competitive crowd all make times faster.

Typical race-day weather

Around March 21 the day usually runs from 31°F at dawn to 51°F in the afternoon, with measurable rain on about 32% of days. Cold snaps dip to 21°F and hot years reach 67°F.

Based on 90 days within a week of the date over the last 5 years, from historical weather for the start area. Not a forecast.

From the race's page

What the organizers of 16th Annual Rock CF Rivers Half Marathon cover on their registration page, in brief.

Schedule and packet pickup

Packet Pickup

Runners can pick up for others. Having QR codes handy will help things move quicker. We will email those out race week! Early Pick Up. Wednesday March 18 & Thursday March 19. Run Detroit (1948 Division St. Suite 105 Detroit, MI). Time…

Schedule and packet pickup

Schedule of Events

Schedule of Events for Rock CF Rivers Half Marathon Race Week! Packet Pick Up. Wednesday, March 18 & Thursday, March 19- RUNdetroit (1948 Division Ste. 105, Detroit, MI 48207). 10:00 am - 6:30 pm. Saturday, March 21- Grosse Ile MIDDLE…

Course

Race Maps

Our interactive Google Map can be found HE RE! Half Marathon. 15K Map. 5K Map. Detailed mapp of the airport area & shuttle parking!

Race Maps, from the 16th Annual Rock CF Rivers Half Marathon page

Parking and travel

Parking

2027 Rock CF Rivers Half Marathon, 15K & 5K Parking Info. 1) Township Shuttle Lots by Grosse Ile Airport: Beginning at 6am to Grosse Ile High School. - Use the address 9801 Intrepid & enter off of Meridian Rd. only. - Please park where…

Shirt and medal

Race Swag

All participants will receive a race medal with their respective distance (including virtual!) as well as a race shirt. Here are some shots of this year's Rock CF Rivers Half Marathon race shirt and medal! 🤘. Don't miss out on your chance…

Race Swag, from the 16th Annual Rock CF Rivers Half Marathon page
Full details on the race's RunSignup page

Race details

Where
7800 Grays Dr, Grosse Ile, MI 48138Map
Course
Road
Start elevation
About 610 feet
Included with entry
T-Shirt; Long Sleeve Tech Shirt
Donations
Accepted when you register
Distances
5K, 15K, Half Marathon
Editions
2027 (Mar 21, 2027), 2026 (Mar 22, 2026), 2025 (Mar 9, 2025)

Organize this race? Add details or a correction

Plan your race

Quick answers

When is 16th Annual Rock CF Rivers Half Marathon?
Sunday, March 21, 2027, starting at 8:00 AM.
How much does it cost?
Entry starts at $40 before processing fees.
When does registration close?
Online registration closes Mar 21, 2027, unless the race fills first.
Is the entry fee high for Michigan?
At $90, entry is about 33 percent above a typical half marathon in Michigan, which costs $67.50 right now.
Do runners get a shirt or medal?
Entry includes a shirt, according to the race's registration page. Check it for sizes and whether kids' races get the same.
Can I donate to a cause when I register?
Yes. The registration form offers an optional donation, usually for the charity or nonprofit the race supports. The race's own page names the cause.
What distances can I run?
5K, 15K, Half Marathon.
How big is it, and how fast?
In 2026, 675 runners finished the Half Marathon; the median finish was 1:57:09 and the winner ran 1:03:19.
Is it a fast course?
The fastest quarter of the 2026 half marathon field finished under 1:41:43, against 1:52:52 in a typical Michigan half marathon, so times here run 10 percent faster.
Where does it start?
7800 Grays Dr, Grosse Ile, MI 48138.

From the organizers

The 16th Annual Rock CF Rivers Half Marathon, 15K, and 5K is coming back to the island of Grosse Ile, Michigan on Sunday, March 21st, 2027 for all to come and help us outrun cystic fibrosis! Starting from the Grosse Ile High School, enjoy the flat-and-fast course en route to chasing a personal best, experiencing your first half marathon, or taking in the scenic views of the Detroit River with friends & family at one of Michigan's premier spring races.