I began this thread less than two years ago and there was a total of 31 zoos in the USA with Polar Bears and now there are 30 zoos with the species. Even with the glut of brand-new exhibits, there was a decline of one zoo due to the recent decision by Indianapolis to send away their remaining bear to Detroit.
I highlighted the zoos with new or modernized exhibits since 2010:
Alaska - NEW exhibit (2017?)
Bronx
Brookfield - NEW exhibit
Buffalo - NEW exhibit
Cincinnati
Columbus - NEW exhibit
Como Park - NEW exhibit
Denver
Detroit
Henry Vilas - NEW exhibit
Kansas City - NEW exhibit
Lincoln Park - NEW exhibit (2017?)
Louisville - NEW exhibit
Maryland
Memphis
Milwaukee County
North Carolina - NEW exhibit
Omaha
Oregon - NEW exhibit (2018?)
Philadelphia
Pittsburgh
Point Defiance - NEW exhibit (2019?)
Rio Grande
Saint Louis - NEW exhibit
San Diego
San Diego SeaWorld
San Francisco
Seneca Park
Toledo
Utah's Hogle - NEW exhibit
Total: 30 American zoos with Polar Bears (including 14 new or modernized exhibits) but overall the population of bears has easily dropped in half from what it was a couple of decades ago. At least 6 zoos (Bronx, Omaha, Oregon, Philadelphia, San Francisco, Seneca Park) are left with only 1-2 elderly bears.