Manteca’s growing attraction as a retirement destination for active seniors played a big role in pushing the city’s population mark to 68,136 in 2011.The city has forwarded information to the Department of Finance noting that 340 net additional housing units were built last year in Manteca. That includes 294 single family homes and 52 apartment units that were built and six single family homes that were demolished.Almost one out of every three new homes sold in Manteca in 2011 were in Del Webb at Woodbridge. The active retirement community caters to those 55 and older.