What makes county population estimates useful is not just the population totals, but the underpinnings of those estimates. Included in the "components of change" are the bureau's year-by-year estimates of the number of people over 65, people under 65, births, deaths, immigrants and domestic migrants (which means people who moved to any county from any other county in the U.S.). This is good fodder for stories about the growth of the elderly and immigration populations, ups or downs in births (best to double-check those with actual birth figures, usually compiled by health departments), and the appeal of your region to people from other parts of the country.
Census has recently published 1996 estimates by county of the age, race and Hispanic origin population. Slap them into a spreadsheet and track change since 1990.
The numbers are not as accurate as the Census, because they are estimates from administrative records rather than results of a door-to-door survey. You should be cautious about using them for very small counties. But they sure beat figures that are nearly a decade old.
Another useful data set – and about to get somewhat more useful – is the International Revenue Service County Migration files. These records count the number of taxpayers and dependents who moved from one county to another in any given year and include their total and median income.