To be in, or to enter, a place casually. The omission of “to be” or “to go” goes back to the fifteenth century; N.E.D.
1757. Happening in company with a colonel of militia, I took occasion, &c.—‘Life of John Woolman,’ 11th day, 5th month.
1800. Some young Americans happening at Toulon.—Weems’s ‘Washington’ (1877), i. 5. (N.E.D.)
1855. Happening into the Suffolk jail on a business errand, we were somewhat startled by hearing our name called.—Boston Bee, Feb. (Bartlett).
1889. Happening into a book auction sale in Boston.—Boston Journal, Oct. 29. (N.E.D.)
