In the 1850s when Harper's began, the theatre was an extremely popular art form in the United States. During the 1857-58 season, a financial panic hit the country, yet the New York Opera reported having its best season ever.
Launching along with Harper's in 1857 was the Broadway hit The Poor of New York, the melodrama by Dion Boucicault that dealt with good and wicked characters alike navigating the effects of financial panic. The show opened at Wallack's Theatre at 485 Broadway (near Broome Street) and immediately produced a sensation by reproducing a burning tenement building right on stage.
Wallack's Theatre was referred to in the press as an "exceedingly elegant little house" catering to those with "the most delicate taste". Over the years, though, fashionable society moved uptown, and so did the theatre. In 1861, the father-and-son team of James and Lester Wallack moved their company up to 844 Broadway at 13th Street. It was here that Boucicault's play The Shaughraun played for 143 performances.
As the center of New York continued to move northward, the company (now just run by Lester, following his father's death) moved uptown again, this time to the corner of 30th Street and Broadway. It is the Wallack's Theatre here (renamed the Germania, and later the Star) that hosted a famous production of The School for Scandal by Richard Brinsley Sheridan featuring John Gilbert as Sir Peter Teazle and Rose Coghlan as his wife Lady Teazle.
Here's a picture that ran in Harper's showing the famous screen scene in the play: