Fair enough; what I know is from what we learn in school, from discussions with people, from my parents and grandparents, and of course in part from media.
You should go and read some history books, assuming you're able to read and comprehend them.
The DDR aka East Germany ended in the 90s, and the Franco regime in Spain ended 1975 with Francos death.
It is debatable if one should also count the Yugoslavian/Serbian government which existed until the mid-90s as oppressive - I certainly do, Miloševic rot in pieces.
Oh, I almost forgot the rest of the Soviet block... so you basically have oppressive regimes as low as 20-30 years ago, leaving a LOT of people with first hand experience.
But typically, the sort of people who blithely compare the US to a police state do so by invoking the Nazis. I wasn't going to credit such arguments with that much subtlety or self-awareness, since they seem to come from a sense of prejudice and knowledge of pop culture rather than history. Although you're right - there are a number of recent police states and dictatorships which the US does not resemble.