That statistic refers to ANY provider within a county. I guess they pick counties as a more reliable source of regional information than say a state (too big) or a city (leaves out rural people and suburban dwellers.)

Statistical info here:
State Abortion Statistics

In brief:
"The U.S. abortion rate is now at the lowest level since 1974, down to 21.3 abortions per 1,000 women aged 15-44 in 2000, according to new research from The Alan Guttmacher Institute (AGI). The number of abortion providers has also fallen, from a high of 2,908 in 1982 to 1,819 in 2000... The number of providers fell in 38 states and the District of Columbia, leaving 87% of counties with no abortion provider... In the Midwest and South, nearly half of women lived in counties with no abortion provider in 2000, while in the Northeast and West, fewer than one in five women lived in such counties. "