The league says 213 of those players were born outside the U.S. and Canada. The U.S. produced 293 players and Canada 24.
The two dozen Canadians represent the largest bloc outside of the U.S. and one more than the 23 from Brazil.
The numbers are ever-changing, however, and all is not always what it seems.
For example, the league lists midfielder Matt Stinson among the Canadians but he was cut last week by Toronto FC. And while Sporting Kansas City forward Teal Bunbury was born in Hamilton, he represents the U.S. internationally.
Toronto FC striker Robert Earnshaw was born in Zambia but plays for Wales. Montreal Impact defender Matteo Ferrari began life in Algeria but represented Italy.
Still the league's foreign reach is impressive.
The letter S alone features players born in St. Kitts & Nevis, Scotland, Serbia, Sierra Leone, South Africa, South Korea, Spain, Sweden and Switzerland.
After the U.S., Canada and Brazil, the next countries on the list are Colombia (19), England (15), France (14) and Jamaica and Mexico (both 12).
Interestingly there are four times as many players from the Democratic Republic of Congo (4) than there are from Germany (1).
Citing data from the Elias Sports Bureau, MLS says its 61 countries represented are the most of the major North American leagues: NBA (44), NHL (19), MLB and NFL (both 16 in 2012).
More imports could join MLS with the primary transfer window not closing until May 6.
The MLS numbers reflect how many players were born abroad but still do not count as internationals.
In 2013, a total of 152 international slots are divided among the 19 clubs. The remaining roster slots must belong to domestic players.
The Montreal Impact, Toronto FC and Vancouver Whitecaps can fill their domestic slots with either Canadian or U.S. players. The Canadian clubs are required to have a minimum of three Canadian domestic players on their rosters.
Players with the legal right to work in Canada are considered Canadian domestic players (Canadian citizen, permanent resident, or part of a protected class, according to the league).
Toronto FC midfielder Julio Cesar (Brazil) and Darel Russell (England), for example, aren't counted as internationals. Both have U.S. green cards.
For clubs based in the United States, a domestic player is either a U.S. citizen, a permanent resident (green card holder) or the holder of other special status (refugee or asylum status).