I'm afraid, Anthony, that the departamental origin of the regiments is not a straightforward matter. I have analysed the origin of the 10,941 soldiers of the 120th line infantry --a regiment that only fought in Spain and that was created in 1808-- and have found that they came from many places:
Dordogne * 865 7.91%
Lot et Garonne * 779 7.12%
Gironde * 716 6.54%
Haute Garonne * 670 6.12%
Charente Inférieure * 669 6.11%
Orne * 356 3.25%
Ariège * 311 2.84%
Gers * 319 2.92%
Rhin et Moselle 0 282 2.58%
Deux Nèthes * 269 2.46%
Pyrénées Orientales * 262 2.39%
Jemappes 0 261 2.39%
Ille et Vilaine * 235 2.15%
Marengo 0 231 2.11%
Calvados * 227 2.07%
Haute Loire * 223 2.04%
Nord * 218 1.99%
Seine et Oise * 205 1.87%
Sarthe * 200 1.83%
Tarn * 189 1.73%
Loire * 184 1.68%
Lot * 166 1.52%
Mont-Tonnerre 0 162 1.48%
Drôme * 158 1.44%
Eure et Loir * 158 1.44%
Stura 0 155 1.42%
Roer 0 138 1.26%
Bouches du Rhône * 132 1.21%
Tarn et Garonne * 132 1.21%
Aude * 130 1.19%
Hautes Pyrénées * 130 1.19%
Cantal * 124 1.13%
Morbihan * 117 1.07%
Var * 114 1.04%
Corrèze * 113 1.03%
Landes * 113 1.03%
Puy de Dôme * 80 0.73%
Aveyron * 61 0.56%
Seine * 57 0.52%
Sambre et Meuse 0 56 0.51%
Doire 0 55 0.50%
Pas de Calais * 55 0.50%
Loiret * 54 0.49%
Côte d'Or * 46 0.42%
Ardèche * 45 0.41%
Haute Saône * 45 0.41%
Basses Pyrénées * 43 0.39%
Creuse * 42 0.38%
Manche * 35 0.32%
Allier * 34 0.31%
Dyle 0 31 0.28%
Indre et Loire * 31 0.28%
Cher * 30 0.27%
Loire Inférieure * 25 0.23%
Lozère * 23 0.21%
Charente * 19 0.17%
Escaut 0 19 0.17%
Moselle * 19 0.17%
Haute Marne * 18 0.16%
Hérault * 17 0.16%
Pô 0 15 0.14%
Somme * 15 0.14%
? 13 0.12%
Haute Vienne * 14 0.13%
Oise * 11 0.10%
Ourte * 11 0.10%
Bas Rhin * 10 0.09%
Rhône * 10 0.09%
Ardennes * 8 0.07%
Côtes du Nord * 8 0.07%
Meurthe * 8 0.07%
Doubs * 7 0.06%
Jura * 7 0.06%
Mayenne * 7 0.06%
Saône et Loire * 7 0.06%
Seine Inférieure * 7 0.06%
Basses Alpes * 6 0.05%
Indre * 6 0.05%
Loir et Cher * 6 0.05%
Lys 0 6 0.05%
Maine et Loire * 6 0.05%
Nièvre * 6 0.05%
Aube * 5 0.05%
Eure * 5 0.05%
Meuse * 5 0.05%
Montblanc 0 5 0.05%
Vendée * 5 0.05%
Vosges * 5 0.05%
Apennins * 4 0.04%
Gard * 4 0.04%
Gênes 0 4 0.04%
Isère * 4 0.04%
Marne * 4 0.04%
Montenotte 0 5 0.05%
Vienne * 4 0.04%
Finistère * 3 0.03%
Golo 0 3 0.03%
Haut Rhin * 3 0.03%
Hautes Alpes * 3 0.03%
Seine et Marne * 3 0.03%
Vaucluse * 3 0.03%
Aisne * 2 0.02%
Deux Sèvres * 2 0.02%
Forêts 0 2 0.02%
Taro 0 2 0.02%
Ain * 1 0.01%
Alpes Maritimes * 1 0.01%
Garonne * 1 0.01%
Hollande 0 1 0.01%
Léman 0 1 0.01%
Méditerranée 0 1 0.01%
Meuse Inférieure * 1 0.01%
Rhône et Loire * 1 0.01%
Yonne * 1 0.01%
(The asterisk denotes current French departéments, the zeros are the Imperial departements or foreign countries).
Hope this helps,
Jorge