The Washington Senators have lost the most games by a team in a month, with 29 losses in July 1909.

	TEAM	L	MONTH	W	L%	G	W%	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	PA	TB	XBH	SH	SF	IBB	GIDP	AVG	OBP	SLG	OPS
1	Senators	29	July 1909	5	.853	35	.147	1,123	56	227	25	11	2		56	6		21		1,225	280	38	40				.202	.244	.249	.493
2	Athletics	28	July 1916	2	.933	30	.067	977	70	222	31	11	2		78	5	128	32		1,088	281	44	28				.227	.288	.288	.575
3	Athletics	27	September 1940	8	.771	35	.229	1,170	126	275	44	9	21	118	103	5	156	13		1,297	400	74	19			25	.235	.300	.342	.642
4	Phillies	27	September 1939	6	.818	33	.182	1,077	100	260	39	11	14	89	87	1	116	17		1,190	363	64	25			34	.241	.299	.337	.636
5	Athletics	27	September 1915	5	.844	33	.156	1,082	113	229	38	24	5		76	5	161	23		1,183	330	67	20				.212	.267	.305	.572
6	Superbas	27	September 1908	6	.818	33	.182	1,077	70	211	23	11	6		62	9		13		1,143	274	40	27				.196	.246	.254	.500
7	Cardinals	27	September 1908	7	.794	34	.206	1,139	85	259	35	11	4		55	8		25		1,228	328	50	26				.227	.268	.288	.556
8	Spiders	27	September 1899	1	.964	28	.036		75
9	Alleghenys	27	August 1890	1	.964	28	.036		113
10	Twins	26	May 1982	3	.897	29	.103	980	89	223	38	6	21	81	73	1	177	7	3	1,065	336	65	1	10	3	20	.228	.279	.343	.622
11	Mets	26	August 1962	8	.765	34	.235	1,185	127	270	31	10	38	120	128	6	230	12	13	1,333	435	79	10	4	8	19	.228	.305	.367	.672
12	Phillies	26	August 1961	7	.788	33	.212	1,112	109	290	32	12	24	102	87	4	153	7	7	1,233	418	68	22	8	5	22	.261	.315	.376	.691
13	Athletics	26	August 1960	9	.743	35	.257	1,214	140	316	46	6	18	129	94	0	169	4	2	1,338	428	70	15	15	2	29	.260	.310	.353	.662
14	Athletics	26	August 1945	8	.765	34	.235	1,189	114	309	42	9	6	100	84	11	83	7		1,310	387	57	26			24	.260	.315	.325	.640
15	Athletics	26	August 1943	3	.897	29	.103	992	88	225	33	8	2	81	66	6	82	17		1,080	280	43	16			21	.227	.279	.282	.561
16	Terrapins	26	September 1915	6	.813	32	.188	1,051	93	241	30	6	4	80	69	9		30		1,159	295	40	30				.229	.283	.281	.563
17	Reds	26	September 1914	4	.867	31	.133	990	82	225	21	9	1	66	84	12	155	37		1,113	267	31	27				.227	.296	.270	.565
18	Spiders	26	August 1899	4	.867	30	.133		108
19	Spiders	26	July 1899	4	.867	30	.133		102
20	Mets	25	July 1963	4	.862	29	.138	957	80	208	24	5	18	74	56	10	183	4	5	1,030	296	47	3	4	3	14	.217	.267	.309	.576
21	Orioles	25	August 1954	7	.781	32	.219	1,073	88	260	44	13	9	81	115	5	139	5	11	1,219	357	66	15	11		34	.242	.316	.333	.648
22	Giants	25	August 1953	10	.714	35	.286	1,215	156	302	47	6	37	150	90	7	150	6	1	1,326	472	90	14			30	.249	.304	.388	.693
23	Senators	25	August 1949	6	.806	31	.194	1,081	95	256	43	3	12	89	106	2	113	5		1,209	341	58	20			23	.237	.306	.315	.622
24	Reds	25	August 1945	7	.781	32	.219	1,110	102	281	46	7	14	97	71	5	122	11		1,197	383	67	11			27	.253	.301	.345	.646
25	Dodgers	25	July 1944	5	.833	30	.167	1,047	117	254	45	9	9	104	90	3	80	5		1,151	344	63	11			19	.243	.304	.329	.633