What Is Illegal Entry to the United States?
U.S. immigration law actually uses the term "improper entry," which has a broad meaning. It's more than just slipping across the U.S. border at an unguarded point. Improper entry can include:
entering or attempting to enter the United States at any time or place other than one designated by U.S. immigration officers (in other words, away from a border inspection point or other port of entry)
eluding examination or inspection by U.S. immigration officers (people have tried everything from digging tunnels to hiding in the trunk of a friend's car)
attempting to enter or obtain entry to the United States by a willfully false or misleading representation or willful concealment of a material fact (which might include, for example, lying on a visa application or buying a false green card or other entry document).
https://www.alllaw.com/articles/nolo/us-immigration/crime-enter-illegally.html