Albert Marth discovered NGC 6661 = m 383 = St II-20 on 6 Jun 1864 and noted "F, vS, R." His RA is accurate and his dec is 1' south. Édouard Stephan rediscovered the galaxy on 16 Jul 1871 and measured a very accurate micrometric position. Stephan must not have had a copy of Marth's discovery list as he independently found quite a few of Marth's objects. NGC 6660, found by Lewis Swift on 14 Jul 1885, is a duplicate observation. See that number.

400/500mm - 17.5" (7/1/89): moderately bright, moderately large, bright core, elongated NW-SE. Located just south of a shallow arc consisting of five mag 12-13 stars and just north of a line of four mag 11 stars oriented SW-NE. Forms a pair with NGC 6658 9.7' WSW.

Notes by Steve Gottlieb