Jen Roth begins to run. She heads west down Nevada Street from the two-story house where her husband Carl grew up and where they now live together with their 7-year-old daughter, Nora. It is a cloudy afternoon and Jen wears a turquoise windbreaker over a long-sleeved t-shirt and black leggings. She takes off at an easy pace. The Brooks Adrenaline GTS 13 shoes she got for a discount online barely make a sound on the brick street.

At 5-foot-4, the 41-year-old doesn’t have the slimmest body. But she doesn’t lack in determination. Today’s goal: 18 miles, her longest run yet toward her goal of racing in the 26.2-mile Christie Clinic Illinois Marathon that was then still five weeks off. The windbreaker comes off after barely half a mile. Jen ties it around her waist alongside her new 20-ounce water bottle. Strapped to her left hand is her iPhone.

She listens to podcasts, not music, and has a playlist more than three hours long, filled with “The Skeptics Guide to the Universe,” “Radiolab” and “Sawbones,” among others. She made the playlist this morning and was somewhat overwhelmed by how long it needed to be for her run.

“It’s not exactly the physical exertion,” she says. “It’s the thought that this is going to take forever. It drives home how long I’m going to be out here.”

Jen’s journey didn’t start on Nevada Street. It started two blocks east on Race Street when she took Nora, then 2, in a stroller to watch the marathon runners go by in 2009. Watching them, she made up her mind: She would run a half marathon the next year. She had been looking for something to keep her in shape. She had lost the baby weight fairly easily, but she hadn’t been working out at all. She had achieved a black belt in taekwondo in 2006, but that passion had run its course and she needed a new exercise goal.

Growing up near Springfield, Jen ran track in high school. The 3,200 meters — two miles — was her best events. She saw the marathon as something to be revered. It was the peak of athletic endurance. At the University of Illinois studying biology in the mid-1990s, her distance running stopped and she hardly worked out at all. She met Carl and they married in 1998. Ever since college her weight had ballooned. She started taekwondo classes and dropped nearly 50 pounds. She kept at it, putting off pregnancy until she had earned her black belt. Then Nora became her life.

“I never went back,” Jen says. “It was hard to find time with an infant. With running, I can work it around other things I have to do, as opposed to having to be there at a specific time. I was getting pretty out of shape.”

It’s hard to say what Jen is chasing: a childhood dream, good health, personal satisfaction. She runs three hours every weekend chasing 26.2 — an arbitrary number steeped in Greek legend and Olympic lore. She doesn’t do it to please anyone but herself. She wants to do it once, so she can forever say she did it, so she can call herself a marathoner.

The route mapped into the RunMeter app on Jen’s phone is the exact route for the marathon. She has ran five half marathons now, her first in 2010, and is familiar with the first half of the local course. It’s the second half, the part that circles through Champaign, that she has never ran and which she is running now.

On First Street, having run about three miles, she heads north toward downtown Champaign. She cuts down Logan Street and has to stop at a couple of lights to wait for traffic. She imagines the street with a crowd of people cheering her on. The sidewalk is surprisingly empty for a Saturday afternoon. She cruises through downtown and heads west down Church Street. RunMeter tells her she is going faster than she anticipated.

I need to slow down a bit, she tells herself.

On a normal day Jen is up at a quarter to seven. She wakes Nora and gets her dressed, then showers while Nora eats breakfast. She, Carl or usually both of them will walk Nora the two blocks to school. Then it’s off to work and school — Jen works in communications for the department of animal sciences and Carl is working on his doctorate in computer science.

Her training regimen has created stress — not only for her. Jen usually works until five, and then, most days, goes running. If Nora has soccer, Jen will pick her up after her run. Carl does most of the cooking. On weekends, she has had to set aside larger and larger chunks of time for her long runs. She started in December with a slow nine-mile run. She has gradually upped that to today’s 18 miles. Her running eats into the time she could be cleaning the layer of dust on the shelves at home or cashing the check that’s been in her wallet for two weeks now.

“I’m behind at work,” she says. “I’m behind on housework. My list of deferred things I want to do gets longer and longer.”

Jen’s running through a residential neighborhood near Lincolnshire Fields Country Club. She’s still going strong until shortly after her ninth mile. Then her breathing gets heavy and she’s audibly gasping. Her shoes pound the pavement harder. She feels as if she is trying to suck air into her lungs through a vacuum hose. She can’t quite get enough. Her pace slows. Her body is heavy: her arms, her legs, even her head.

On Branch Road, a younger man in a gray sweatshirt passes her running the same direction. The man runs at a pretty fast clip. He gets smaller and smaller ahead of her. She watches him turn up Blackthorn Drive and knows he must be practicing the same route she is. Before long he is gone.

Her first half marathon was hell. It was muggy from an early morning thunderstorm and Jen had to walk five of the 13.1 miles. She doesn’t remember her time other than that it was slow. She was going to give a full marathon a shot in October, but tendinitis limited her training time. She ran another half instead. The race was her best yet: 2 hours and 17 minutes. It’s an average time. Her goal for the full is 4:30. Again, an average time.

But her time isn’t her main concern. She doesn’t care if she has to walk part of the race. She likes telling people she is running a marathon. She likes the new tone in her leg muscles. She likes that 13.1 miles, which used to be her limit, seems like nothing now. Still, she doesn’t anticipate enjoying the last few miles on race day. The closest thing she can compare running a marathon to is pregnancy. It was scary at first, seemingly impossible, and now she just wants it to be done.

“Of course, there’s a difference between it’s done and you have a baby, and it’s done and you have a ton of free time,” she says, laughing. As race day has neared, Jen has gotten worn out. Yet she’s in her best shape in years. “I’ve enjoyed getting to this point. Knowing I can set my mind to doing something hard and actually doing it is a big deal.”

After 15 miles, Jen has caught her second wind. She feels light again. She passes the 16-mile marker and is now running the farthest she has ever run. Back on campus, she picks up the pace to catch the light at Peabody and Sixth. She runs through the South Quad and finally stops on Nevada, when RunMeter tells her she has reached 18 miles. She walks the rest of the way home, her breathing slowly calming.

Of today’s run, she says, “I’m pretty pleased about it.”

After months of running through winter cold and spring rain, Jen finally came to the Christie Clinic Illinois Marathon. It was a sunny, 82-degree day. She ran the race in 5:10, 40 minutes slower than her goal. She had to walk portions of the course, but she completed all 26.2 miles. When she finished, she wanted nothing but to go to sleep. She was stiff everywhere, and the walk back to her car took so long she found it almost comical.

But for Jen, it was worth the time and pain, the hour runs after work and the three-hour runs on her days off. She doesn’t think her first marathon will be her last. The end result was too satisfying: She is a marathoner.

“I was a little down because I had to walk more than I’d hoped and because my time was so slow,” Jen says days after the race. “But that feeling didn’t last long. Mostly, I was just really, I don’t know, content. It just made me feel really at peace with myself.”

Sean can be reached at [email protected] or @sean_hammond.