The 1937-S is one of the key dates of the Washington quarter series in both circulated and mint state grades. In the 1960s, when markets were made in circulated rolls of all better date then modern coins, a roll of circulated 1937-S quarters was a "hot" item. In fact, in circulated condition, this issue was considered the third rarest of the series after only the 1932-D and 1932-S. The buyers focused on the fact that this issue is the third lowest mintage of the series...and probably rightly so. Today, an argument can be made that the 1934-D and 1935-D are as rare or rarer in circulated condition. They certainly are rarer in Gem condition. In mint state condition, and in Gem MS65 or better for that matter, the 1937-S is about tied with the 1935-S as the second rarest S-Mint Washington quarter with only the 1932-S being rarer. While this issue is not common in Gem condition, it is not as rare as the 1934-D, 1935-D, 1936-D, and of course the 1932-D and 1932-S.
The 1937-S was occasionally available by the roll in uncirculated condition in the 1960s and 1970s, but was much less available than most of the other issues of the 1930s. You can find frosty white, well-struck Gems and truly superb specimens are occasionally available.
The 1937-S Washington Quarter is the third lowest mintage quarter in the series. It is also considered one of the key dates in the series because of its low mintage. At the time it was struck, people were already collecting Uncirculated rolls of coins and thanks to them, many Uncirculated examples of this issue still exist today.
Due it its low mintage and Uncirculated examples being saved early on, the coins were always very difficult to find in circulation. In low grades it commands about 5 times more than the generic dates in the series and in Uncirculated grades it commands even higher premiums than the most common dates.