I think I see the problem. There's a "Groveland Township" which includes Pekin and Morton and East Peoria. That easily could add up to 18,000 back in the 2006 Census. But I thought this node referred to the village of Groveland itself, which is around 1400 people. I'll check if the node represents the village or the township and adjust accordingly, cause I do still see the 18,000 in the OSM data and in CoMaps.