How did Kacey Musgraves get to be such a New York City slicker?

On the gloomiest of nights, with rain pouring over the city, the country-pop darling somehow got a crowd of jaded New Yorkers to put on the sunniest of smiley faces at Radio City Music Hall in the second of two sold-out shows.

Welcome to the Cult of Kacey. Check your New York attitude at the door and get transported to a blissfully happy place where you do singalongs with strangers and embrace your corny instead of your cool.

How do I know? Well, this was my third Kacey Musgraves show in New York in less than nine months, so consider me converted.

First there was the Beacon Theatre in January, just two weeks before she won four Grammys — including the coveted Album of the Year — for her resplendent “Golden Hour.” Second, there was her set at Governors Ball on Randall’s Island Park, where — as the only country act at the festival on its middle Saturday — she outshined everyone from alt-rock (Florence + the Machine), hip-hop (Vince Staples) and EDM (Major Lazer).

Then there was Wednesday night. In the penultimate date on her “Oh, What a World: Tour II,” Musgraves was, in all likelihood, playing her last theater show in New York before graduating to the Garden and other local arenas. And she had the big-city crowd entranced by her small-town country.

Everyone was on their feet — some in kitschy, neon-rimmed cowboy hats — for the duration of the show, even for the slowest of numbers. And during songs such as “Wonder Woman,” “Butterflies” and “Lonely Weekend,” people sang, swayed and snuggled (if they were lucky) along as if they could care less about the city outside of Musgraves’ world. This was a safe place for hipsters to let down their hip, for grinders to slow their grind.

While there isn’t anything technically striking about Musgraves’ voice, she has a beautiful tone that is remarkable for its simplicity and purity. And it makes her songs perfect for audience singalongs without fear of being side-eyed by the concertgoer next to you.

Nor would you be be judged for being your most basic, authentic self in the Cult of Kacey. Which Musgraves drove home with “Follow Your Arrow,” her pro-LGBTQ anthem from 2013’s “Same Trailer, Different Park,” which won Song of the Year at the 2014 CMA Awards.

Promoting inclusivity in country — a genre that isn’t exactly known for it — it was the kind of rainbow that you could see even on the gloomiest of nights.