County government offices are located at 105 East Main Street, Rock Port MO 64483; phone: 660-744-6562.
Organized February 14, 1845, from Holt County and named for David Rice Atchison, United States senator. The boundaries for Allen County were defined by the legislature in 1843 and attached to Holt County in 1845. Atchison County was organized out of this territory and the act defining Allen County repealed. The first settler in the area is believed to be Major Stephen Cooper who arrive about 1836
The county seat (Rock Port City) was reported in April 2008 to be the first town in the U.S. to have it's total electricity needs supplied by 4 wind-powered generators. In fact, it's anticipated that the wind farm will generate excess power which will be sold to a public utility. Rock Port's population is approximately 1,400 citizens who occupy approximately 700 housing units. (County population is approximately 6,300.)