Perhaps one of ABC's first truly popular daytime series, along with the game show Let's Make a Deal (which had moved from its original home NBC in 1968), Dark Shadows found its demographic niche in teenagers coming home from school in time to watch the show at 4 p.m. Eastern/3 p.m. Central, where it aired for almost all of its network run, the exception being a 15-month stretch between April 1967 and July 1968, when it aired a half-hour earlier. Originally, it was aired in black-and-white, but the show went into color starting with the episode broadcast on August 11, 1967. It became one of ABC's first daytime shows to win the rating for its timeslot, leading to the demise of NBC's original Match Game and Art Linkletter's long-running House Party on CBS, both in 1969.
Dark Shadows began with a 4.1 rating in the 1965–66 TV season, tying for thirteenth place out of eighteen daytime dramas. The audience figures only improved slightly, to 4.3, in 1966–67. 1966 was a volatile year for soaps, and many ended their runs between the premiere date of Dark Shadows in June and the month of December. By that time, six months had passed, and Dark Shadows had failed to gain major traction. In June, it ranked #13 out of 18 soaps, and by December, the lower-rated offerings were gone and the show officially ranked #13 out of 13 soaps. "The show was limping along, really limping", head writer Sam Hall remembered, "and ABC said, 'We're canceling it. Unless you pick up in 26 weeks, you're finished.' [Series creator Dan Curtis] had always wanted to do a vampire picture, so he decided to bring a vampire — Barnabas Collins — to the series."
Barnabas (Jonathan Frid) was introduced in April 1967. With a time slot change to 3:30 Eastern/2:30 Central, many more teenagers found the program. By May 1968, the series was still in last place (out of 12 offerings), but rose to a 7.3 rating, the rough equivalent of gaining the viewership of three million households in the span of one year. Dark Shadows returned to its 4 p.m. Eastern/3 p.m. Central time slot in July 1968, without losing much of its audience. One Life to Live, which was launched by ABC in July 1968 in the 3:30 slot, also sought to reach the newfound young demographic.
The series reached its peak in popularity during a storyline set in the year 1897, broadcast from March 1969. By the end of May, Dark Shadows was ABC's most popular soap opera, and by late 1969 it was reaching between 7 and 9 million viewers on any given day, and ranking 11th out of a total 15 daytime dramas in that time period.