Star Trek: The Original Series (NBC): Ratings Recap

'Star Trek: The Original Series' premiered September 8, 1966 to a 20.7 HH rating representing 11.36 million homes. The show averaged an 18.8 rating on Thursday nights over the course of its first season, enough to warrant a second season. A second season aired on Fridays, averaging a slightly lower 15.8 rating though the season's penultimate episode delivered the highest audience of its run with a 21.6. A third and final season fell to a 13.3 rating on-average and the finale managed just an 8.8. 

There were a variety of companies that published ratings in the era that this show aired, including Nielsen, Arbitron, and Trendex, and even within Nielsen there were several data streams released including the Overnights, MNAs, and Pocketpiece. There's a great write-up about all of this at the Star Trek Fact Check blog. This data all comes from the NTI Pocketpieces which represent the "final" national U.S. ratings.

Star Trek: The Original Series Season 1 Ratings (1966-67)
Episode Date	HH Rating	HHs (mil.)
Sept. 8, 1966	20.7	11.36
Sept. 15, 1966	18.4	10.10
Sept. 22, 1966	18.9	10.38
Sept. 29, 1966	18.3	10.05
Oct. 6, 1966	16.5	9.06
Oct. 13, 1966	17.9	9.83
Oct. 20, 1966	17.1	9.39
Oct. 27, 1966	16.3	8.95
Nov. 3, 1966	18.1	9.94
Nov. 10, 1966	17.4	9.55
Nov. 17, 1966	17.3	9.50
Nov. 24, 1966	18.6	10.21
Dec. 8, 1966	15.7	8.62
Dec. 15, 1966	15.5	8.51
Dec. 29, 1966	18.4	10.10
Jan. 5, 1967	16.2	8.89
Jan. 12, 1967	19.7	10.82
Jan. 19, 1967	19.2	10.54
Jan. 26, 1967	20.0	10.98
Feb. 2, 1967	18.3	10.05
Feb. 9, 1967	19.9	10.93
Feb. 16, 1967	18.1	9.94
Feb. 23, 1967	20.0	10.98
Mar. 2, 1967	18.4	10.10
Mar. 9, 1967	18.9	10.38
Mar. 23, 1967	17.3	9.50
Mar. 30, 1967	17.0	9.33
Apr. 6, 1967	17.1	9.39
Apr. 13, 1967	17.7	9.72
Average	18.0	9.90

Star Trek: The Original Series Season 2 Ratings (1967-68)
Episode Date	HH Rating	HHs (mil.)
Sept. 15, 1967	12.8	7.17
Sept. 22, 1967	14.6	8.18
Sept. 29, 1967	15.1	8.46
Oct. 6, 1967	13.6	7.62
Oct. 13, 1967	14.1	7.90
Oct. 20, 1967	13.8	7.73
Oct. 27, 1967	15.8	8.85
Nov. 3, 1967	14.7	8.23
Nov. 10, 1967	12.7	7.11
Nov. 17, 1967	13.0	7.28
Dec. 1, 1967	15.6	8.74
Dec. 8, 1967	17.7	9.91
Dec. 15, 1967	16.4	9.18
Dec. 22, 1967	-	-
Dec. 29, 1967	15.6	8.85
Jan. 5, 1968	19.5	10.92
Jan. 12, 1968	17.8	9.97
Jan. 19, 1968	16.9	9.46
Feb. 2, 1968	17.0	9.52
Feb. 9, 1968	18.1	10.14
Feb. 16, 1968	14.9	8.34
Feb. 23, 1968	15.7	8.79
Mar. 1, 1968	15.7	8.79
Mar. 8, 1968	15.6	8.74
Mar. 15, 1968	21.6	12.10
Mar. 29, 1968	15.7	8.79
Average	15.8	8.83

Star Trek: The Original Series Season 3 Ratings (1968-69)
Episode Date	HH Rating	HHs (mil.)
Sept. 20, 1968	16.1	9.18
Sept. 27, 1968	11.7	6.67
Oct. 4, 1968	13.3	7.58
Oct. 11, 1968	14.0	7.98
Oct. 18, 1968	12.9	7.35
Oct. 25, 1968	13.5	7.70
Nov. 1, 1968	14.0	7.98
Nov. 8, 1968	13.2	7.52
Nov. 15, 1968	13.4	7.64
Nov. 22, 1968	13.0	7.41
Nov. 29, 1968	15.3	8.72
Dec. 6, 1968	17.3	9.86
Dec. 20, 1968	13.7	7.81
Jan. 3, 1969	12.0	6.84
Jan. 10, 1969	13.9	7.92
Jan. 17, 1969	11.9	6.78
Jan. 24, 1969	13.7	7.81
Jan. 31, 1969	14.2	8.09
Feb. 14, 1969	12.2	6.95
Feb. 21, 1969	12.4	7.07
Feb. 28, 1969	13.3	7.58
Mar. 7, 1969	11.8	6.73
Mar. 14, 1969	13.0	7.41
Jun. 3, 1969	8.8	5.02
Average	13.3	7.57

*Week of Dec. 18-24, 1967 was a Nielsen "Black Week" with no ratings

Source: Nielsen Media Research NTI Pocketpieces