Uganda had a population of 7 million when it gained independence in 1962, and is currently at 43 million. It's projected to reach 90 million people (and be the world's 20th most populous country) by 2050.
It has a land area of less than 200,000 sq km (less than 77,000 sq mi).

Nigeria had a population of 45 million in 1960, which has since more than quadrupled to over 200 million. That is projected to double in the next 30 years, becoming the 4th most populous country in the world.

Half a century ago, Ethiopia had less than 30 million people. The current population is about 110 million. It's expected to have close to a quarter of a billion people by 2050.

Congo-Kinshasa/Zaire/DRC had a population of 15 million in 1960. Despite decades of ethnic conflict killing & displacing millions, this is projected to have increased by almost a factor of 10 in less than a century: 145 million by 2050. The current population is 100 million.

Kenya gained independence in 1963 with a population of 9 million. It currently has around 50 million, expected to increase by another 20 million in the next 30 years.

Niger had a little over 3 million people in 1960. Despite having less than 660 sq km of arable land, and being subject to recurrent droughts, it currently sustains a population of almost 25 million, expected to reach over 60 million by 2050.

The population of Sudan has quadrupled from 1970 to today, and is currently over 40 million (with another 11 million in the successor state of South Sudan). This is expected to grow by another 20 million in the next 30 years in Sudan, and another 9 million in South Sudan.

Ghana had only 11 million people in 1980, a figure which has almost tripled in the last 40 years (almost 32 million currently). Ghana is expected to have 56 million inhabitants by 2050.

Côte d'Ivoire (Ivory Coast) had only 3.5 million inhabitants when it gained independence in 1960. It currently has over 25 million people, a figure which is expected to double in the next 30 years.

The population of South Africa has increased from 22 million in 1970 to 60 million today. Despite having the highest number of HIV+ people in the world, and a stagnant white population growth, the number is expected to increase by another 15 million in the next 30 years.

Chad, which is mostly Sahara or Sahel, had only 3 million people at independence in 1960. The current population is 15 million, expected to more than double by 2050.

Liberia was home to only 1 million in 1960. Current population is over 5 million, expected to reach 10 million by 2050. This may seem relatively small, but keep in mind its history of endless ethnic conflict, slavery, cannibalism, child soldiers, civil war & resource struggles.

Senegal had a population of around 3 million at independence in 1960, and 16 million today. This is expected to double by 2050.

Barely 10 million people lived in Angola as recently as the mid 1980s. Today the country has over 30 million, expected to more than double to almost 70 million by 2050.

Some 5 million people lived in Guinea in 1980. In the past forty years, that has tripled to almost 15 million. That number will increase by at least another 10 million by 2050.

Tanzania had a population of 10 million in 1960. Almost 60 million today. Will be almost 120 million in 2050, a population which will be greater than Turkey, Japan, Iran and Vietnam at that point.
I could keep going but I think we all get the picture.