Kennilworth, on Chicago's North Shore, was No. 1 and Beverly Hills, Calif., came in 37th in a study identifying the 50 wealthiest American suburbs. Pierre deVise, an urbanologist with Roosevelt University in Chicago, based his research on projections of 1985 per capita income from 1983 census data. The Kennilworth figure was $48,950, compared to $31,337 in Beverly Hills. In second place was Hunter's Creek, Tex., near Houston ($47,956). Southern California also was represented by Rancho Santa Fe near San Diego, ranked eighth at $41,756, Marina del Rey ($32,750) in 28th place and San Marino ($30,459) 41st.