Factual error: Periodically Indiana's "DMV" is mentioned, however, unlike most states, Indiana has a 'Bureau of Motor Vehicles' (BMV), not a 'Department of Motor Vehicles' (DMV).
Factual error: Leslie mentions that Eagleton is "2 towns over." We in later episodes see the border wall between them (S3E12), indicating they're right next to each other.
The Treaty - S4-E7
Factual error: At the UN conference, 'England' is shown as a member of the Security Council. England sits on both the UN and the Security Council as part of the 'United Kingdom' - not as a stand-alone country. UN nerds Leslie and Ben would have known this.