If you want to see a key milestone in the life and career of Boston-area Celtic musician Adam Hendey, just go to his YouTube.

One day in 2020, Hendey and his then-fiancé Frannie Monahan took a little excursion to the Chestnut Hill Reservoir, found a pleasant spot overlooking the water, and – with the help of Monahan’s brother – recorded footage for a video to accompany Hendey’s rendition of the traditional song “Ten Thousand Miles.”

That video was, essentially, Hendey’s debut as a singer.

“Although I've always loved accompanying singers, I hadn’t put myself forward in that way,” he recalls. “But when I was home during the initial COVID lockdowns, I decided to pick up singing and just give it a go. I started making these recordings of arrangements of songs, and then I had the idea to make that video and post it on YouTube. I really think of it as an important first step.”

Almost exactly six years later, Hendey is set to hit another milestone: On September 21 at Club Passim in Harvard Square, he’ll officially launch his new album, “Illuminate.” Joined by Monahan and numerous friends, Hendey fully leans into his vocalist persona on six of the album’s nine tracks, with interpretations of traditional ballads and songs as well as two Hendey originals that draw on folk tradition, and a cover of Rachel Anne Goodman’s “Elk River Blues.” The remaining tracks feature Hendey-composed instrumentals plus a rendition of the popular traditional Irish jig “Lark in the Morning.”

It’s been a rather eventful time for Hendey since that day at the Chestnut Hill Reservoir. On the personal side, he and Monahan – after having arrived in Boston in 2018 – left for Los Angeles in 2021, got married, returned to Boston in 2022 and, last January, became parents. Along the way, Hendey (who also now sports a distinctive mustache) settled in as one of the more active, high-profile figures in Boston’s Celtic music scene, performing at venues and events like Club Passim, BCMFest and the Burren’s Brian O’Donovan Legacy Series, and bringing his DADGAD-style guitar to sessions at The Burren, McCarthy’s, Emmet’s, the Irish Cultural Centre of Greater Boston, The Druid and Bunratty Tavern, to name a few.  

“Illuminate” represents a convergence of several threads in Hendey’s life, going back to his teenage years when he attended a summer Celtic music camp in California, which was where he first met Monahan. Finding his groove as a singer steeped in the folk music tradition has been gratifying for Hendey, who also plays whistle, bass, bouzouki and mandolin, and has lately added sean-nos dancing to his talents. The album also showcases his aptitude for sound design – creating, acquiring and manipulating audio elements for music recordings, films and other media – for which he carries the credential of a degree from the University of Oregon. At various points on “Illuminate,” Hendey stacks multiple layers of voices or instruments to widen and deepen the aural dimension. Elsewhere, he adds assorted sounds that unobtrusively complement the music: crows, church bells, cannons, and various birds including crows, seagulls and – appropriately enough – blackbirds and thrushes; one song ends with a recording of his son’s in-utero heartbeat.     

“I love folk ballads so much, and I've always kind of received them as a listener in a very cinematic way, as a movie-going experience,” says Hendey, whose first album in 2016 was all-instrumental. “I also love the idea that, through arrangement and instrumentation and orchestration, you can pull emotional levers – that’s something I’ve really enjoyed exploring. And for ‘Illuminate,’ because I produced it myself, there was no one to stop me from going crazy. No one could hold me back from adding four electric guitars to a track, or including cannons or ocean sounds.”

Hendey’s voice has an acute warmth and gentleness to it, notably on the metaphor-heavy “Blackbirds and Thrushes” (which he learned as a graduate student at the Royal Conservatoire of Scotland) and “Handsome Blue,” his reimagining of the “Sweet Willie”/female-sailor storyline. But he can evoke drama and tension where appropriate, such as on his “Counting Game,” a call-and-response ditty in cantering 7/8 that verges between playful romance and something more ominous, or “Castle by the Sea,” a variant of “Lady Isabel and the Elf Knight” (a ballad in the my-boyfriend-is-a-serial-killer mold) that is set in Boston. 

Yet another facet of “Illuminate” is that it pulls together a representative sample of the most recent generation to make its presence felt in Boston’s folk/acoustic community. The guest musicians include Hendey’s concert band of Elias Cardoso, Brendan Hearn and Erin Shea Hogan – some of whom have their own bands that include Hendey and others on the album (an organizational chart would be nearly illegible). Hogan, who sings on five tracks, provides a most effective counterpart to Hendey, whether ratcheting up narrative intensity or enhancing the sheer emotionality of a verse or refrain – especially on the winsome “Blackbirds and Thrushes,” which also includes backing vocals by Monahan, Cardoso, Helen Kuhar (Hogan’s bandmate in the quartet Forsyth) and Conor Hearn (Brendan Hearn’s brother and half of the duo Rakish); another Forsyth member, Kate Knudsvig, contributes soulful fiddle. 

 But there’s no overlooking the instrumental/non-vocal aspects of “Illuminate.” Hendey’s skill on various guitars and whistles is evident (his rhythmic touch on “Handsome Blue,” for example), as are those of the contributing musicians, notably Cardoso (fiddle, accordion) and Hearn (cello). And rather than simply provide a continual wall of sound throughout, the instrumental backing surges and subsides relative to the individual character of each song – as demonstrated amply on “Castle by the Sea.” 

The instrumental sets also show Hendey’s flair for composition and orchestration: The 7/8 “To the Moon and Back” leads with a supple whistle over chugging guitar and Hearn’s growling cello, then gets a charge from Cardoso’s fiddle and Hendey’s step dancing before segueing into the fleet 4/4 “Mystic River.”  “Chrysanthemum” is more pensive, a sharp-edged electric guitar and bass set against bowed strings and overdubbed whistles. 

“Lark in the Morning,” which closes out the album, is an appropriate coda: While Hendey and crew don’t exactly present the four-part jig “session style,” there is a sense of a circle growing as other musicians join in – locals Simon Lace (tenor banjo) and Noah Kelly (fiddle), along with Oregon-based uilleann piper Eliot Grasso, a longtime friend and collaborator of Hendey.   

“I'm very allergic to telling people what to do,” Hendey says. “I really try to just create a sound environment of people with similar instincts and similar tastes and just let it happen. On stage, there aren't super-specific arranged lines that I've instructed people to play. But for the album, I got a little bit more specific with people. When Brendan and Elias, for instance, were in the studio with me tracking their string parts, I had a little talk mic in my control room and I would sing parts to them and then they would play them. We would just build up these big string arrangements line by line. 

“Similarly, with the other singers, particularly Erin, I’d say, ‘Can you try this?’ and then sing lines – and she’d sing them significantly better than me, which was great.” 

Assembling the various components that eventually resulted in “Illuminate” took a while, says Hendey – as far back as 2020 and that video shoot with Monahan at Chestnut Hill Reservoir. The six years encompass personal growth as well as musical development, and at the nexus of these was his settling into the Boston-area music community of which he is a fixture.

“I think I have well and truly become a New Englander now. But there's a lot of Californian roots in me that will never go away,” he says. “And that’s all right. I feel fortunate to have both be a part of me.” 

For more about Adam Hendey and “Illuminate,” see adamhendey.com