Active ballparks in bold type, and ranked. Parks no longer in use (regardless of whether they're still standing) in normal type with an asterisk.
Ties broken by most recent. For those that have not yet hosted, ties broken by most LCS hosted, then most LDS, then age (newest, therefore gone less without having hosted, to oldest, therefore gone longer).
For each stadium, I am using its best-remembered name, not necessarily its current name.
* Yankee Stadium, New York (opened in 1923, torn down in 2010), 37: 1923, 1926, 1927, 1928, 1932, 1936, 1937, 1938, 1939, 1941, 1942, 1943, 1947, 1949, 1950, 1951, 1952, 1953, 1955, 1956, 1957, 1958, 1960, 1961, 1962, 1963, 1964, 1976, 1977, 1978, 1981, 1996, 1998, 1999, 2000, 2001, 2003.
* Polo Grounds, New York (1911-1964), 13: 1911, 1912, 1913, 1917, 1921, 1922, 1923, 1924, 1933, 1936, 1937, 1951, 1954. No, 1921 and 1922 don't get counted twice because the Yankees and Giants both made it and both then used the Polo Grounds.
* Sportsman's Park (1909-1967, the 1st stadium to be known as Busch Stadium), St. Louis, 10: 1926, 1928, 1930, 1931, 1934, 1942, 1943, 1944, 1946, 1964. No, 1944 doesn't get counted twice because both St. Louis teams made it and both used Sportsman's Park.
1. Fenway Park, Boston (1912), 9: 1912, 1914, 1946, 1967, 1975, 1986, 2004, 2007, 2013. The Braves used Fenway in 1914, because it was larger than the South End Grounds. They opened Braves Field the next year, and invited the Red Sox to use their new larger stadium for World Series home games in 1915, 1916 and 1918, which is why Fenway didn't host a World Series between 1914 and 1946.
* Ebbets Field, Brooklyn (1913-1960), 9: 1916, 1920, 1941, 1947, 1949, 1952, 1953, 1955, 1956.
2. Dodger Stadium, Los Angeles (1962), 8: 1963, 1965, 1966, 1974, 1977, 1978, 1981, 1988.
* Connie Mack Stadium, Philadelphia (1909-1976), 8: 1910, 1911, 1913, 1914, 1929, 1930, 1931, 1950. Known as Shibe Park from 1909 to 1952.
* Busch Stadium, St. Louis (1966-2005), 6: 1967, 1968, 1982, 1985, 1987, 2004.
3. Wrigley Field, Chicago (1914), 6: 1929, 1932, 1935, 1938, 1945, 2016. The Cubs used the White Sox' larger Comiskey Park for their World Series games in 1918, but not in 1910. (See West Side Park, below.)
4. Oakland Coliseum (1966), 6: 1972, 1973, 1974, 1988, 1989, 1990.
* Tiger Stadium, Detroit (1912-2006), 6: 1934, 1935, 1940, 1945, 1968, 1984. Known as Navin Field from 1912 to 1937, and Briggs Stadium from 1938 to 1960.
* Memorial Stadium, Baltimore (1954-2002), 6: 1966, 1969, 1970, 1971, 1979, 1983.
* Riverfront Stadium, Cincinnati (1970-2002), 5: 1970, 1972, 1975, 1976, 1990.
5. Kauffman Stadium, Kansas City (1973), 4: 1980, 1985, 2014, 2015.
6. AT&T Park, San Francisco (2000), 4: 2002, 2010, 2012, 2014.
* Shea Stadium, New York (1964-2008), 4: 1969, 1973, 1986, 2000.
* Atlanta-Fulton County Stadium (1965-1997), 4: 1991, 1992, 1995, 1996.
* Crosley Field, Cincinnati (1912-1972), 4: 1919, 1939, 1940, 1961.
* Forbes Field, Pittsburgh, 4 (1909-1971): 1909, 1925, 1927, 1960.
* Comiskey Park, Chicago (1910-1991), 4: 1917, 1918, 1919, 1959.
* Braves Field, Boston, 4 (1915-1955): 1915, 1916, 1918, 1948.
* West Side Park, Chicago (1885-1920), 4: 1906, 1907, 1908, 1910.
7. Jacobs/Progressive Field, Cleveland (1994), 3: 1995, 1997, 2016.
8. Busch Stadium, St. Louis (2006), 3: 2006, 2011, 2013.
* Veterans Stadium, Philadelphia (1971-2004), 3: 1980, 1983, 1993.
* Milwaukee County Stadium (1953-2001), 3: 1957, 1958, 1982.
* Griffith Stadium, Washington (1911-1965), 3: 1924, 1925, 1933.
* Bennett Park, Detroit (1896-1911), 3: 1907, 1908, 1909.
9. Comerica Park, Detroit (2000), 2: 2006, 2012.
10. Globe Life Park, Arlington (1994), 2: 2010, 2011.
11. Citizens Bank Park, Philadelphia (2004), 2: 2008, 2009.
* Sun Life Stadium, Miami (1987, still used for college & pro football), 2: 1997, 2003.
* Jack Murphy Stadium, San Diego (1967, still used for college & pro football), 2: 1984, 1998.
12. SkyDome, Toronto (1989), 2: 1992, 1993.
* Metrodome, Minneapolis (1982-2014), 2: 1987, 1991.
* Candlestick Park, San Francisco (1960-2015), 2: 1962, 1989.
* Three Rivers Stadium, Pittsburgh (1970-2001), 2: 1971, 1979.
* Cleveland Municipal Stadium (1931-1996), 2: 1948, 1954.
13. Citi Field, New York (2009): 1, 2015.
14. Yankee Stadium, New York (2009), 1: 2009.
15. Tropicana Field, St. Petersburg (1990), 1: 2008.
16. Coors Field, Denver (1995), 1: 2007.
17. U.S. Cellular Field, Chicago (1991), 1: 2005.
18. Minute Maid Park, Houston (2000), 1: 2005.
19. Angel Stadium, Anaheim (1966), 1: 2002.
20. Chase Field, Phoenix (1998), 1: 2001.
21. Turner Field, Atlanta (1997), 1: 1999.
* Metropolitan Stadium, Minneapolis (1956-1985), 1: 1965.
* Los Angeles Memorial Coliseum (1923, still used for college football), 1: 1959.
* League Park, Cleveland (1910-1951), 1: 1920.
* Baker Bowl, Philadelphia (1895-1950), 1: 1915.
* South Side Park, Chicago (1890-1940), 1: 1906.
* Columbia Park, Philadelphia (1901-1912), 1: 1905.
* Polo Grounds, New York (1890-1911), 1: 1905.
* Exposition Park, Pittsburgh (1890-1915), 1: 1903.
* Huntington Avenue Grounds, Boston (1901-1912), 1: 1903.
22. Oriole Park at Camden Yards, Baltimore (1992): 3 ALCS, 1996, 1997, 2014.
23. Nationals Park, Washington (2008): 2 NLDS, 2012, 2014.
24. Safeco Field, Seattle (1999): 2 ALCS, 2000, 2001.
25. Great American Ballpark, Cincinnati (2003): 2 NLDS, 2010, 2012.
26. Miller Park, Milwaukee (2001): 2 NLDS, 2008, 2011.
27. PNC Park, Pittsburgh (2001): 1 NLDS, 2013.
28. Target Field, Minneapolis (2010): 1 ALDS, 2010.
29. Petco Park, San Diego (2004): 1 NLDS, 2006.
30. Marlins Park, Miami (2012): No postseasons in 4 years.
That the Mets were dead last among active ballparks, until their Pennant this season moved them all the way up to 13th, is a quirk, due to having a relatively new stadium. That the Yankees are 14th among active ballparks is a shock, but remember: Like Citi Field, the new Yankee Stadium only opened in 2009.
*
By City:
1. New York (including Brooklyn): 66
(Bronx separately: 37)
2. St. Louis: 19
3. Chicago: 16
4. Philadelphia: 15
5. Boston: 14
(Manhattan separately: 14)
6. San Francisco (including Oakland): 12
7. Detroit: 11
8. Los Angeles (including Anaheim): 10
9. Cincinnati: 9
(Los Angeles separately: 9)
(Brooklyn separately: 9)
10. Pittsburgh: 7
11. Cleveland: 6
(San Francisco separately: 6)
(Oakland separately: 6)
12. Baltimore: 6
13. Atlanta: 5
(Queens separately: 5)
14. Kansas City: 3
15. Minneapolis: 3
16. Milwaukee: 3
17. Washington: 3
18. Dallas: 2
19. Miami: 2
20. San Diego: 2
21. Toronto: 2
22. Tampa Bay: 1
23. Denver: 1
24. Houston: 1
(Anaheim separately: 1)
25. Phoenix: 1
26. Seattle: 0
By State:
1. New York: 66 (Last in 2015)
2. California: 24 (2014)
3. Missouri: 22 (2015)
4. Pennsylvania: 22 (2009)
5. Illinois: 16 (2016)
6. Ohio: 15 (2016)
7. Massachusetts: 14 (2013)
8. Michigan: 11 (2012)
9. Maryland: 6 (1983)
10. Georgia: 5 (1999)
11. Texas: 3 (2011)
12. Florida: 3 (2008)
13. Minnesota: 3 (1991)
14. Wisconsin: 3 (1982)
15. District of Columbia: 3 (1933)
16. Colorado: 1 (2007)
17. Arizona: 1 (2001)
Canada: 2 (Both in Ontario, 1993)