Walter E. Lonergan (September 22, 1885 – January 23, 1958) was a second baseman in Major League Baseball who played briefly for the Boston Red Sox during the 1911 season. Listed at 5 ft 7 in (1.70 m), 156 lb., Lonergan batted and threw left-handed. He was born in Boston, Massachusetts.
In a 10-game career, Lonergan was a .269 hitter (7-for-26) with two runs, one RBI, and one stolen base. He did not have any extra-base hits. In nine fielding appearances, he committed three errors in 39 chances for a .923 fielding percentage.
Lonergan died in Lexington, Massachusetts, on January 23, 1958 at age 72.