Visit https://coinmarketcap.com/currencies/tether/markets/ and then find "Contracts" On the "More" dropdown button, you can see which blockchains are supported, as of now it includes in 23 cryptocurrencies.

To see the full picture of what Tether actually is, you can refer to their FAQs page: https://tether.to/en/faqs and [UPDATED]PSA: Most Stablecoins Can Be Frozen, Even in Your Own Wallets also worth to take a look.