40 Home Run seasons by franchise.

Franchise includes stuff like:
Oakland As: also when they played in Philadelphia and Kansas City
Atlanta Braves: also when they played in Boston and Milwaukee
Baltimore Orioles: also when they were the St. Louis Browns
Minnesota Twins: also when they played in Washington as the Nationals and Senators
Texas Rangers: previously the new Washington Senators who replaced the "Twins" 1961-1971
Washington Nationals: also when they were the Montreal Expos

Some of those previous incarnations had no player hit 40 but the search was inclusive.

Note: the Kansas City Royals  started in 1969 and are the only team which has never had a player hit at least 40 home runs in a season.

Pete Alonso will be 4th Met to hit 40 home runs. Thursday, August 15, 2019

The Mets started in 1962. Even when Alonso hits number 40, the Mets will still have, in addition to the Royals, only three franchises with fewer 40 HR seasons:
Florida started in 1997
Arizona started in 1997
Tampa Bay started in 1993

The first player to hit 40 ... Babe Ruth: 54 in 1920, his first season with the Yankees. Previous high: 29 hit by Ruth in 1919 with the Red Sox in a short season. Ruth zoomed right through being the first to hit 30 and 40.

Sorted by the number seasons a franchise had a player who hit at least 40 home runs, obviously, including multiple times by some players. Details in a future post.

qry40HRbyFranchiseCounts

CountOfplayerID	franchID	franchName	MaxOfHR	MinOfHR	MinOfyearID	MaxOfyearID
31	NYY	New York Yankees	61	40	1920	2017
22	ATL	Atlanta Braves	51	40	1953	2006
22	SFG	San Francisco Giants	73	40	1929	2004
19	BOS	Boston Red Sox	54	40	1936	2018
19	CHC	Chicago Cubs	66	40	1930	2005
18	TEX	Texas Rangers	57	40	1968	2018
15	CIN	Cincinnati Reds	52	40	1953	2007
14	SEA	Seattle Mariners	56	40	1993	2016
14	OAK	Oakland Athletics	58	42	1932	2018
14	TOR	Toronto Blue Jays	54	40	1986	2016
13	LAD	Los Angeles Dodgers	49	40	1951	2004
13	COL	Colorado Rockies	49	40	1995	2016
13	PHI	Philadelphia Phillies	58	40	1923	2009
12	STL	St. Louis Cardinals	70	41	1922	2010
12	CHW	Chicago White Sox	49	40	1993	2016
12	CLE	Cleveland Indians	52	40	1936	2006
11	DET	Detroit Tigers	58	40	1937	2013
10	MIN	Minnesota Twins	49	41	1957	2016
8	BAL	Baltimore Orioles	53	40	1961	2016
8	MIL	Milwaukee Brewers	50	41	1979	2016
7	PIT	Pittsburgh Pirates	54	40	1947	1973
6	HOU	Houston Astros	47	42	1997	2006
4	ANA	Los Angeles Angels of Anaheim	47	40	2000	2015
4	WSN	Washington Nationals	46	42	1999	2015
4	SDP	San Diego Padres	50	40	1996	2009
3	NYM	New York Mets	41	40	1996	2006
2	FLA	Florida Marlins	59	42	1996	2017
2	ARI	Arizona Diamondbacks	57	44	2001	2009
1	TBD	Tampa Bay Rays	46	46	2007	2007