Earlier this year, Sufjan Stevens released Carrie & Lowell, his seventh studio album which was roundly lauded as his best work. But the definitive Sufjan album—the one that best exemplifies his ambition, his cinematic scope, even his silliness—is 2005's Illinois, which came out 10 years ago this week.

Where Carrie & Lowell was born from a place of intimate mourning, with Stevens channeling the grief from his mother's death, Illinois originated as pure artifice. A continuation of the ludicrous "50 States Project," a semi-jokey attempt, that began with 2003's Michigan, to chronicle the vastness of the entire country, one album at a time. It was a traveling salesman gimmick, but it brought out the grandeur in his songwriting—regional folklore unearthing universal emotions.

-=-=-=-A multi-instrumentalist with a music theory background, Stevens has always composed with an appropriate breadth—his discography branches from electronic chaos (2001's Enjoy Your Rabbit) to folky, minimalist spirituals (2004's Seven Swans). But with Illinois, that endless experimentation coalesced into a more comprehensive and satisfying sprawl. "I always like to think of my performances as sounding like a sixth-grade band," he admitted in a hilariously dated MTV News "You Hear It First" report. Indeed, some Illinois expanses feel like they originated in the frantic brain of a middle-school musical prodigy. As he did with Michigan, Stevens played over a dozen instruments himself, from his reliable oboe to guitars and keys. Illinois is nuanced, due in part to the diverse overdub team he employed while piecing the songs together.

Rob Moose, co-founder of New York City classical ensemble yMusic, played an integral role in the sessions, crafting lush string arrangements for tracks like "Chicago" and "They Are Night Zombies!! They Are Neighbors!! They Have Come Back from the Dead!! Ahhhh!" He met Stevens in 2004 after being introduced by My Brightest Diamond's Shara Worden, then a member of Stevens' touring band. The violinist later knocked out "something like 10 songs" in three hours in the living room of a Washington Heights apartment.

"[Stevens] seemed serious and curious, mellow but controlling, haphazard," Moose reflects. "We did the string session with a four-track and some cheap mics, Sufjan engineering. He later told me he never listened back until much later and realized that only the violin one and cello mic worked. My signal was really loud, so he turned it off."

"Sufjan had everything scribbled out," Moose says of the album’s string arrangements. "There are one or two tracks that are just the string quartet. It sounds kind of ragged but awesome. I think it was one of the first sessions I ever did. He basically tacked it onto a My Brightest Diamond rehearsal we were having and just used those players because he knew Shara. I got an email earlier that week saying he wanted a few hours of our time and had a hundred dollars for us. My friend seemed excited about that, and I thought she was crazy. A hundred dollars? But I was 22, so I did it. I'll never forget seeing Little Miss Sunshine and hearing the strings from 'Chicago' featured prominently in one scene, and thinking back on that paycheck. I told Sufjan about it; he said 'best hundred dollars I ever spent.'"

Drummer James McAlister first entered Stevens' orbit in 2003, joining the "Michigan Militia" touring band after an introduction from singer-songwriter Denison Witmer. (Twelve years later, McAlister's still performing with Stevens—most recently developing stage-friendly percussion arrangements for the Carrie & Lowell material.) But they established their musical chemistry on Illinois during a three-day recording sprint at The Buddy Project in Queens. Using a cheap digital 8-track, Stevens led the percussionist through challenging, unorthodox sessions wherein McAlister played drums to the singer's Wurlitzer piano—and nothing else.