Here's how many people are old enough to vote in this year's election, and how they are spread across the United States, along with figures on the total population. Generally, in the most recent elections when the presidency was at stake, only about half of those who were old enough to vote actually went to the polls. For example, according to the Census Bureau, turnout in the 1984 presidential election was only 53.1 percent of the voting-age population, up from 52.6 percent in 1980. The bureau said turnout was 62.8 percent in 1960, 61.9 percent in 1964, 60.9 percent in 1968, 55.1 percent in 1972, and 53.6 percent in 1976. The last census in 1980 placed the nation's total population at 226,546,000, and the next such official count will be in 1990. Meantime, the Census Bureau's most recent detailed estimates are that total population reached 243,400,000 in mid-1987 and that 182,628,000 residents will be at least 18 years old when America votes this November. Since the 1984 presidential election, the voting-age population is estimated to have grown by more than 8 million. The bureau points out that voting-age projections are based on the resident population of the United States including members of the armed forces where they reside at their duty stations. It said these projections exclude people overseas _ about 520,000 in the military and 65,000 federal civilian workers plus their dependents of voting age, and an unknown number of other American citizens residing abroad _ who would be eligible to vote by absentee ballot in their home state. Meanwhile, the bureau said that the population of voting age includes many who meet the age requirement but cannot vote. Because citizenship is a universal requirement for voting, aliens are the main group of ineligible voting-age people, the bureau said. About 6.5 million legal aliens and 2.5 million undocumented aliens age 18 or over are included in the estimates and represent roughly 5 percent of the total population of voting age, the bureau said. The bureau also said somewhat more than 680,000 people will be ineligible to vote because they will be in prisons or mental hospitals. Based on Census Bureau reports, here is a state-by-state list covering: _Total population figures from the census on April 1, 1980. _An estimate of what the total population had reached on July 1, 1987, the latest available such list. _An estimate of this November's voting-age population (residents aged 18 or over), from projections released in February as a reference for the current election season.