As an immigrant or dual citizen, do I need an estate plan in both the US and my home country?

Possibly. If you own assets in more than one country, a single will may not cleanly govern property abroad, since each country applies its own succession and probate rules, and some nations impose forced-heirship laws that override your wishes. Many people in this situation use coordinated wills, one for U.S. assets and one for foreign assets, carefully drafted so they don't accidentally revoke each other. Cross-border estates can also face double taxation and complex reporting, and a non-citizen spouse may need special planning such as a QDOT to access the marital estate-tax deferral. This is not a DIY area. Work with an attorney experienced in international estates in each relevant country, and revisit the plan if your residency, citizenship, or asset locations change.