One of the main economic problems for any country with an overpopulation problem is the shortage of food, minerals, fuel and other resources. This applies particularly to third world countries where harvest failure and famine are frequent. Populations which survive on subsistence farming are particularly badly hit, as without their crops and animals they will starve. Such people are only able to support themselves in the most basic way, and do not have disposable income to pay taxes with. The result of this sort of overpopulation is that there is no money in the country's kitty or treasury to provide social security, pensions or a basic health service for a burgeoning population. Some countries have even put a limit on the number of children families can have.
Overpopulation means that more goods are required to support the population. When overpopulation occurs it also means that there is not enough supplies to sustain the population. There is a shortage of goods and supplies. There is also usually a shortage of water.
Education is another major concern related to overpopulation. Educating too many children becomes an issue. It can lead to a reduction in funds available for schools and teachers as well. Classrooms become overcrowded and children do not receive a high quality education.
Another major concern with overpopulation is housing all of these people. Sometimes it can be difficult to find places for all of these people to live.
While the first answer is somewhat correct, a growing population does not necessarily mean that demand will grow faster than supply.
In some ways, there is no such thing as overpopulation. There can only be too much population compared to economic capacity.
If there are too many people compared to a country's economic capacity, the country will experience low GDP per capita. It will probably have poor human resources (lack of education, for example) and will have low productivity.
When a term like "overpopulation" is used, it automatically implies that the population of people in the economy is more than what can be supported by the economy in terms of providing full employment and a reasonable standard of living.
The capability of an economy to employment is dependent on existence of a base of capital assets that need people for its operation. An economy that is overpopulated does not have enough of such capital assets. Further the rate of increase of such capital assets by way of installation of new industries in he economy is slow because the saving rate is lower. The total production in such economy is consumed by more people than are required to generate such production, thereby lowering lower per capita income, which tends to reduce the saving percentage. Thus it becomes difficult for economy to grow fast.
Overpopulation generally means there will more demand.
The economic problem of scarcity will become more serious as supply of necessities such as natural resources are limited.