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Ever heard someone call some place or some situation a "ZOO?"  Like, "Wow, it's a total zoo out there?"  Meaning confusing or chaotic?  No doubt you have heard it or said it your self, but in reality most zoo's are pretty organized and pretty chill.

That's because they have had lots of time to practice.

On this day, July first of 1874, 145 years ago, the Philadelphia Zoological Society, the first zoo in the U.S., opened its doors.  The Philadelphia Zoo is still the Top 20 of American Zoos.

You may not support the idea of exotic animals in cages or enclosures but there is no doubting their national popularity.

According to Travel & Leisure, "Approximately 175 million people—half of America’s population—visit a zoo or aquarium each year...(that's) according to the AZA, a nonprofit accreditation organization. And more than 3.2 million choose the San Diego Zoo, making it the most popular in America. The appeal, according to Steve Feldman, spokesperson for the AZA, is natural: People are hardwired to connect with other species and animals.”

Zoo's can be amazingly affordable adventures.  Admission prices to most zoos are less than movie tickets, and sometimes free.   If  you're ready to go, there's a Top 15 Zoo just 3 hours away in Portland.  Children 2 and under, free; children 3–11, $7.50; ages 12–64, $10.50; seniors 65 and up, $9; oregonzoo.org.

See which animals and attractions have drawn millions of people to the 20 most popular zoos in America starting with the most popular zoo in San Diego.