Randy Johnson and Sandy Koufax struck out over 400 in a season.

Since 1901 only two pitchers struck out at least 400 batters, including World Series and tournament: Randy Johnson and Sandy Koufax.

Johnson 2001: (372+9+19+19)=419

Koufax 1965: (382+29)=411

Since 1901 three pitchers held the season record for SO:

Rube Wadell 1904: 349 in 383 innings: 8.20 per 9 innings
Sandy Koufax 1965: 382 in 336: 10.24
Nolan Ryan 1973 (first year of DH): 383 in 326: 10.57 (#14 among 300 SO seasons)

Bob Feller 1946, only season >=300: 348 in 371: 8.43

Since 1901 at least 300 SO occurred 34 times, including multiples by individuals, led by six each for Randy Johnson and Nolan Ryan; three each for Koufax and Curt Schilling; two: Wadell, Walter Johnson, Sam McDowell, J.R. Richard, Pedro Martinez.

Oldest: Ryan 42 in 1989, then Randy Johnson 38, 37, 36, 35
Youngest: Vida Blue 21 in 1971 (21 of 34 younger than 30)

Most innings: Wadell 383 (14 of 34 >=300)
Fewest innings: Martinez 213 (20 of 34 fewer than 300)

23 of the 34 has SO9 greater than 9.

1901 to 2015, SO>=300 sorted by greatest Strikeouts per 9 IP:

Rk	Player	SO9	SO	Year	Age	Tm	Lg	G	GS	CG	SHO	GF	W	L	W-L%	SV	IP	H	R	ER	BB	ERA	FIP	ERA+	HR	BF	AB	2B	3B	IBB	HBP	SH	SF	GDP	SB	CS	PO	BK	WP	BA	OBP	SLG	OPS	OPS+	Pit	Str
1	Randy Johnson	13.41	372	2001	37	ARI	NL	35	34	3	2	1	21	6	.778	0	249.2	181	74	69	71	2.49	2.13	188	19	994	890	33	2	2	18	10	5	17	19	15	4	1	8	.203	.274	.309	.583	50	4076	2638
2	Pedro Martinez	13.20	313	1999	27	BOS	AL	31	29	5	1	1	23	4	.852	0	213.1	160	56	49	37	2.07	1.39	243	9	835	780	38	0	1	9	3	6	11	21	10	0	0	6	.205	.248	.288	.536	35
3	Randy Johnson	12.56	347	2000	36	ARI	NL	35	35	8	3	0	19	7	.731	0	248.2	202	89	73	76	2.64	2.53	181	23	1001	900	45	2	1	6	14	5	15	26	16	6	2	5	.224	.288	.356	.643	63	4021	2595
4	Randy Johnson	12.12	329	1998	34	TOT	ML	34	34	10	6	0	19	11	.633	0	244.1	203	102	89	86	3.28	2.90	135	23	1014	907	38	1	1	14	5	2	13	31	19	3	2	7	.224	.300	.344	.644	71
5	Randy Johnson	12.06	364	1999	35	ARI	NL	35	35	12	2	0	17	9	.654	0	271.2	207	86	75	70	2.48	2.76	184	30	1079	993	28	4	3	9	4	3	14	42	17	5	2	4	.208	.266	.335	.601	55
6	Clayton Kershaw	11.64	301	2015	27	LAD	NL	33	33	4	3	0	16	7	.696	0	232.2	163	62	55	42	2.13	1.99	175	15	890	839	26	2	1	5	4	0	8	7	9	9	3	9	.194	.237	.284	.521	49	3392	2303
7	Randy Johnson	11.56	334	2002	38	ARI	NL	35	35	8	4	0	24	5	.828	0	260.0	197	78	67	71	2.32	2.66	195	26	1035	945	42	5	1	13	4	2	19	19	15	3	2	3	.208	.273	.346	.619	59	3991	2620
8	Pedro Martinez	11.37	305	1997	25	MON	NL	31	31	13	4	0	17	8	.680	0	241.1	158	65	51	67	1.90	2.39	219	16	947	860	24	4	5	9	9	1	16	20	5	3	1	3	.184	.250	.277	.526	42
9	Nolan Ryan	11.32	301	1989	42	TEX	AL	32	32	6	2	0	16	10	.615	0	239.1	162	96	85	98	3.20	2.51	124	17	988	867	28	2	3	9	9	5	4	36	6	0	1	19	.187	.275	.283	.557	56
10	Curt Schilling	11.29	319	1997	30	PHI	NL	35	35	7	2	0	17	11	.607	0	254.1	208	96	84	58	2.97	2.62	143	25	1009	930	49	7	3	5	8	8	16	9	9	3	1	5	.224	.271	.372	.643	71
11	Curt Schilling	10.97	316	2002	35	ARI	NL	36	35	5	1	0	23	7	.767	0	259.1	218	95	93	33	3.23	2.40	140	29	1017	974	32	8	1	3	5	2	11	9	6	0	0	6	.224	.251	.362	.613	57	3721	2630
12	Randy Johnson	10.86	308	1993	29	SEA	AL	35	34	10	3	1	19	8	.704	1	255.1	185	97	92	99	3.24	3.05	135	22	1043	913	37	3	1	16	8	7	16	28	12	2	2	8	.203	.290	.322	.612	64
13	Sam McDowell	10.71	325	1965	22	CLE	AL	42	35	14	3	5	17	11	.607	4	273.0	178	80	66	132	2.18	2.08	161	9	1116	963	30	0	7	6	13	2	23	4	9	2	0	17	.185	.286	.244	.531	56
14	Nolan Ryan	10.57	383	1973	26	CAL	AL	41	39	26	4	2	21	16	.568	1	326.0	238	113	104	162	2.87	2.49	123	18	1355	1172	53	5	2	7	7	7	24	37	10	4	0	15	.203	.302	.303	.605	78
15	Nolan Ryan	10.43	329	1972	25	CAL	AL	39	39	20	9	0	19	16	.543	0	284.0	166	80	72	157	2.28	2.49	128	14	1154	973	25	3	4	10	11	3	17	40	9	1	0	18	.171	.291	.246	.537	70
16	Nolan Ryan	10.35	327	1976	29	CAL	AL	39	39	21	7	0	17	18	.486	0	284.1	193	117	106	183	3.36	2.91	99	13	1196	990	33	8	2	5	13	4	12	44	23	6	2	5	.195	.322	.284	.606	84
17	Nolan Ryan	10.26	341	1977	30	CAL	AL	37	37	22	4	0	19	16	.543	0	299.0	198	110	92	204	2.77	3.12	141	12	1272	1027	23	3	7	9	22	10	21	43	19	7	3	21	.193	.329	.256	.585	64
18	Sandy Koufax	10.24	382	1965	29	LAD	NL	43	41	27	8	2	26	8	.765	2	335.2	216	90	76	71	2.04	1.93	160	26	1297	1205	29	7	4	5	13	3	13	16	4	1	0	11	.179	.227	.280	.507	52
19	Curt Schilling	10.05	300	1998	31	PHI	NL	35	35	15	2	0	15	14	.517	0	268.2	236	101	97	61	3.25	2.77	134	23	1089	1000	56	6	3	6	14	7	18	10	5	0	0	12	.236	.282	.373	.655	74
20	Mike Scott	10.00	306	1986	31	HOU	NL	37	37	7	5	0	18	10	.643	0	275.1	182	73	68	72	2.22	2.16	161	17	1065	976	41	5	6	2	8	6	11	41	12	2	0	3	.186	.242	.291	.533	53
21	Nolan Ryan	9.93	367	1974	27	CAL	AL	42	41	26	3	1	22	16	.579	0	332.2	221	127	107	202	2.89	2.98	118	18	1392	1165	38	6	3	9	12	4	24	28	21	3	0	9	.190	.313	.279	.592	76
22	J.R. Richard	9.90	303	1978	28	HOU	NL	36	36	16	3	0	18	11	.621	0	275.1	192	104	95	141	3.11	2.51	106	12	1139	979	33	8	4	2	13	4	14	34	14	6	3	16	.196	.298	.283	.580	74
23	J.R. Richard	9.64	313	1979	29	HOU	NL	38	38	19	4	0	18	13	.581	0	292.1	220	98	88	98	2.71	2.21	130	13	1175	1051	38	7	5	3	14	8	17	28	10	1	1	19	.209	.277	.296	.573	65
24	Sam McDowell	8.97	304	1970	27	CLE	AL	39	39	19	1	2	20	12	.625	0	305.0	236	108	99	131	2.92	3.07	134	25	1257	1107	31	6	10	7	8	4	23	2	11	5	0	17	.213	.299	.320	.619	74
25	Sandy Koufax	8.86	306	1963	27	LAD	NL	40	40	20	11	0	25	5	.833	0	311.0	214	68	65	58	1.88	1.85	159	18	1210	1135	28	6	7	3	13	1	9	11	1	0	1	6	.189	.230	.271	.501	54
Rk	Player	SO9	SO	Year	Age	Tm	Lg	G	GS	CG	SHO	GF	W	L	W-L%	SV	IP	H	R	ER	BB	ERA	FIP	ERA+	HR	BF	AB	2B	3B	IBB	HBP	SH	SF	GDP	SB	CS	PO	BK	WP	BA	OBP	SLG	OPS	OPS+	Pit	Str
26	Sandy Koufax	8.83	317	1966	30	LAD	NL	41	41	27	5	0	27	9	.750	0	323.0	241	74	62	77	1.73	2.07	190	19	1274	1178	38	5	4	0	11	8	13	13	5	1	0	7	.205	.252	.294	.545	62
27	Vida Blue	8.68	301	1971	21	OAK	AL	39	39	24	8	0	24	8	.750	0	312.0	209	73	63	88	1.82	2.20	183	19	1207	1103	28	3	3	4	9	3	23	7	7	0	1	10	.189	.251	.272	.523	55
28	Bob Feller	8.43	348	1946	27	CLE	AL	48	42	36	10	5	26	15	.634	4	371.1	277	101	90	153	2.18	2.16	151	11	1512	1331				3	25	0	16	16	11	2	0	3	.208	.291
29	Rube Waddell	8.39	302	1903	26	PHA	AL	39	38	34	4	1	21	16	.568	0	324.0	274	109	88	85	2.44	1.87	125	3	1291					8							0	9	undef	undef	undef
30	Rube Waddell	8.20	349	1904	27	PHA	AL	46	46	39	8	0	25	19	.568	0	383.0	307	109	69	91	1.62	1.59	165	5	1496					14							0	8	undef	undef	undef
31	Steve Carlton	8.06	310	1972	27	PHI	NL	41	41	30	8	0	27	10	.730	0	346.1	257	84	76	87	1.97	2.01	182	17	1351	1244	44	5	8	1	9	9	23	22	12	5	2	8	.207	.257	.291	.548	60
32	Walter Johnson	7.61	313	1910	22	WSH	AL	45	42	38	8	3	25	17	.595	1	370.0	262	92	56	76	1.36	1.39	183	1	1367					13							0	21	undef	undef	undef
33	Walter Johnson	7.39	303	1912	24	WSH	AL	50	37	34	7	13	33	12	.733	2	369.0	259	89	57	76	1.39	2.03	240	2	1413					16							0	11	undef	undef	undef
34	Mickey Lolich	7.37	308	1971	30	DET	AL	45	45	29	4	0	25	14	.641	0	376.0	336	133	122	92	2.92	2.85	124	36	1538	1415	49	8	2	7	12	12	22	18	10	2	0	7	.237	.285	.360	.645	84

Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 2/28/2016.