https://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_populationThe D.R. Congo has a population of 99 million and no freeways. In fact they only have 3,300 km (2,000 mi) of paved roads, no other country comes close with population / paved road ratio. West Africa has improved substantially on this indicator over the past 15 years.
The next largest country with no freeways is Tanzania (pop 61M). Dar es Salaam has some flyovers, but no roads that could be considered bona fide freeways.
The smallest country with freeways (or at least some controlled-access highways) is probably Iceland. Iceland doesn't have formal motorways, but they do have some controlled-access divided highways with at least four lanes.
The next smallest country with a bona fide motorway is Montenegro, followed by Luxembourg, which is the smallest country to have an actual network of motorways (156 km, six separate routes).