The 2010 data counted a statewide population of 897,934 people, a 14.6% increase over the 2000 Census count.

I calculated statewide mean and median population centroids for 2000 and 2010 from the respective Census block polygon shapefiles. The centroid table links (above) also include 1990 population centroids calculated from block group polygons, plus lat-lon equivalents for all centroids.

The centroids of individual Census blocks are readily derived from ArcGIS's "Calculate Geometry" tool. Using DE State Plane (NAD 1983 HARN meters) coordinates, I calculated the state mean population centroid coordinates as the population-weighted arithmetic means of all the individual Census block centroid coordinates. This can be thought of as the gravitational balance point for the state's population.

Between 2000 and 2010 Delaware's mean population centroid moved 4,268 meters southward from 187485W, 155124N to 187919W, 150879N--still in New Castle County, but only 722 meters from the Kent County boundary.

I also calculated median population centroids from the 2000 and 2010 Census block datafiles. This involved sorting the block features by the X field, calculating cumulative percentages of population living west of each X value, and determining the 50th percentile's X value; then sorting the blocks by the Y field, calculating cumulative percentages of population living south of each Y value, and determining the 50th percentile's Y value. Exactly half of Delaware's population live north of the median centroid and half live south of it; half live east of it and half live west of it.

The 2010 median population centroid is located in the Delaware estuary at 185822W, 179203N, 1,604 meters north of the northern tip of Pea Patch Island. The median centroid moved 3,847 meters south from the 2000 median population centroid which was located at 185971W, 183047N.

I used the same procedures with Census block land areas as weights to determine Delaware's mean and median geographic centroids, which are located in southern Kent County. Delaware's geographic mean centroid ("center of balance") is at 192254W, 109811N. The state's geographic median centroid is at 189241W, 100255N. Half of Delaware's land area is north of this point, and half south of it; half is east of this point and half west of it.

The county maps referenced above show the paths of mean and median population centroids for each county between 1990 and 2010. The New Castle County map also shows the 6-7 kilometer southward movement of the statewide population centroids between 1990 and 2010. New Castle County's population centroids have shifted SSW about 4 kilometers over the past 20 years as Wilmington lost population while the MOT area had the fastest population growth. Kent County's population centroids SW of Dover exhibit much slower northwestward movement since the county's fastest growth has occurred just west of Dover. Sussex County's population centroids have shifted 4-5 kilometers eastward due to strong growth in the beach communities.