evidence: Border officials encountered 11 million unauthorized migrants attempting to enter the US between October 2019 and June 2024. Data on these border encounters — which include people attempting to enter the country or apprehended trying to cross the border without inspection — helps the government estimate the number of individuals illegally entering the US. [...] While there isn’t any definitive data on unauthorized immigrant numbers — there’s no way to know how many people entered the US without an encounter — border encounter numbers serve as a helpful if imperfect proxy. The at-the-border apprehension rate helps the Office of Immigration Statistics model what proportion of illegal entries are prevented by apprehensions.