As the enrollment information is from 2010/2011, there are bound to be quite a few changes due to the rise and fall of enrollments...
but my guess at the rough cut-offs, and how many schools will change classifications:
Division 1 ~ 600 or 605 students (about 45 boys and 48 girls teams moving up)
270 WEST HOLMES 305 AAA 302 AAA 607
271 WHITEHALL-YEARLING 306 AA 300 AA 606
271 SHAWNEE 289 AAA 317 AAA 606
271 BAY 265 AA 341 AA 606
274 CARROLLTON 307 AAA 298 AAA 605
275 CARROLL 320 AA 281 AA 601
276 PERKINS 312 AAA 288 AAA 600
277 ORANGE 300 AA 296 AA 596
278 GOSHEN 306 AA 289 AA 595
278 MIAMI TRACE 302 AAA 293 AAA 595
280 NOTRE DAME-CATHEDRAL LATIN 288 AA 306 AA 594
Division 2 ~ 290 (about 56 boys and 55 girls schools moving down, while about 40 boys and 47 girls schools move up)
541 PURCELL MARIAN 156 A 141 A 297
541 WHEELERSBURG 155 AA 142 AA 297
541 CLARK MONTESSORI 146 A 151 A 297
544 MOUNT GILEAD 147 A 149 A 296
544 MIAMI EAST 143 A 153 A 296
546 CENTERBURG 146 A 149 A 295
546 WEST LIBERTY-SALEM 142 A 153 A 295
548 FREDERICKTOWN 144 A 150 A 294
549 EAST KNOX 165 A 128 A 293
549 SOUTHEASTERN 149 AA 144 AA 293
549 HORIZON SCIENCE ACADEMY 148 A 145 A 293
552 LOUDONVILLE 150 A 142 A 292
553 DIXIE 158 A 133 A 291
553 HUNTINGTON 153 AA 138 AA 291
553 EAST PALESTINE 147 A 144 A 291
556 CRESTVIEW 138 AA 152 AA 290
557 OBERLIN 151 A 137 A 288
557 NORTH ADAMS 143 AA 145 AA 288
559 SUMMIT COUNTRY DAY 129 A 158 AA 287
560 MEMORIAL 149 A 137 A 286
560 NEWCOMERSTOWN 148 AA 138 AA 286
560 LYNCHBURG-CLAY 143 AA 143 AA 286
563 PEEBLES 142 AA 143 AA 285
564 COLUMBIA 150 A 133 A 283
564 DAWSON-BRYANT 136 A 147 AA 283
which would mean about 45 boys and girls schools move down from D2 to D3.
In looking at school enrollments, Ohio seems to have smaller school than I thought there would be... Ohio's Division 1 covers Washington's 4A, 3A, and half of the 2A classification enrollments (or in other words, only the top third of Ohio's schools are about as big as the top 45% of Washington's).