diff --git a/app/models/prefill_params.rb b/app/models/prefill_params.rb
index 33261a8ac..37beddd11 100644
--- a/app/models/prefill_params.rb
+++ b/app/models/prefill_params.rb
@@ -56,10 +56,7 @@ class PrefillParams
     end
 
     def to_h
-      {
-        id: champ.id,
-        value: value
-      }
+      { id: champ.id }.merge(champ_attributes)
     end
 
     private
@@ -67,8 +64,14 @@ class PrefillParams
     def valid?
       return true unless NEED_VALIDATION_TYPES_DE_CHAMPS.include?(champ.type_champ)
 
-      champ.value = value
+      champ.assign_attributes(champ_attributes)
       champ.valid?(:prefill)
     end
+
+    def champ_attributes
+      TypesDeChamp::PrefillTypeDeChamp
+        .build(champ.type_de_champ)
+        .transform_value_to_assignable_attributes(value)
+    end
   end
 end
diff --git a/app/models/types_de_champ/prefill_epci_type_de_champ.rb b/app/models/types_de_champ/prefill_epci_type_de_champ.rb
new file mode 100644
index 000000000..9213aff3f
--- /dev/null
+++ b/app/models/types_de_champ/prefill_epci_type_de_champ.rb
@@ -0,0 +1,23 @@
+class TypesDeChamp::PrefillEpciTypeDeChamp < TypesDeChamp::PrefillTypeDeChamp
+  def possible_values
+    departements.map { |departement| "#{departement[:code]} (#{departement[:name]})" }
+  end
+
+  def example_value
+    departement_code = departements.pick(:code)
+    epci_code = APIGeoService.epcis(departement_code).pick(:code)
+    [departement_code, epci_code]
+  end
+
+  def transform_value_to_assignable_attributes(value)
+    return { code_departement: nil, value: nil } if value.blank? || !value.is_a?(Array)
+    return { code_departement: value.first, value: nil } if value.one?
+    { code_departement: value.first, value: value.second }
+  end
+
+  private
+
+  def departements
+    @departements ||= APIGeoService.departements.sort_by { |departement| departement[:code] }
+  end
+end
diff --git a/app/models/types_de_champ/prefill_type_de_champ.rb b/app/models/types_de_champ/prefill_type_de_champ.rb
index 5e9e55380..a385ea653 100644
--- a/app/models/types_de_champ/prefill_type_de_champ.rb
+++ b/app/models/types_de_champ/prefill_type_de_champ.rb
@@ -11,6 +11,8 @@ class TypesDeChamp::PrefillTypeDeChamp < SimpleDelegator
       TypesDeChamp::PrefillRegionTypeDeChamp.new(type_de_champ)
     when TypeDeChamp.type_champs.fetch(:departements)
       TypesDeChamp::PrefillDepartementTypeDeChamp.new(type_de_champ)
+    when TypeDeChamp.type_champs.fetch(:epci)
+      TypesDeChamp::PrefillEpciTypeDeChamp.new(type_de_champ)
     else
       new(type_de_champ)
     end
@@ -33,4 +35,8 @@ class TypesDeChamp::PrefillTypeDeChamp < SimpleDelegator
   def too_many_possible_values?
     possible_values.count > POSSIBLE_VALUES_THRESHOLD
   end
+
+  def transform_value_to_assignable_attributes(value)
+    { value: value }
+  end
 end
diff --git a/spec/models/prefill_params_spec.rb b/spec/models/prefill_params_spec.rb
index 057e70d7d..1354dcaa6 100644
--- a/spec/models/prefill_params_spec.rb
+++ b/spec/models/prefill_params_spec.rb
@@ -72,12 +72,12 @@ RSpec.describe PrefillParams do
       context "when the type de champ is authorized (#{type_de_champ_type})" do
         let(:types_de_champ_public) { [{ type: type_de_champ_type }] }
         let(:type_de_champ) { procedure.published_revision.types_de_champ_public.first }
-        let(:champ_id) { find_champ_by_stable_id(dossier, type_de_champ.stable_id).id }
+        let(:champ) { find_champ_by_stable_id(dossier, type_de_champ.stable_id) }
 
         let(:params) { { "champ_#{type_de_champ.to_typed_id}" => value } }
 
-        it "builds an array of hash(id, value) matching the given params" do
-          expect(prefill_params_array).to match([{ id: champ_id, value: value }])
+        it "builds an array of hash matching the given params" do
+          expect(prefill_params_array).to match([{ id: champ.id }.merge(attributes(champ, value))])
         end
       end
     end
@@ -86,12 +86,12 @@ RSpec.describe PrefillParams do
       context "when the type de champ is authorized (#{type_de_champ_type})" do
         let(:types_de_champ_private) { [{ type: type_de_champ_type }] }
         let(:type_de_champ) { procedure.published_revision.types_de_champ_private.first }
-        let(:champ_id) { find_champ_by_stable_id(dossier, type_de_champ.stable_id).id }
+        let(:champ) { find_champ_by_stable_id(dossier, type_de_champ.stable_id) }
 
         let(:params) { { "champ_#{type_de_champ.to_typed_id}" => value } }
 
-        it "builds an array of hash(id, value) matching the given params" do
-          expect(prefill_params_array).to match([{ id: champ_id, value: value }])
+        it "builds an array of hash matching the given params" do
+          expect(prefill_params_array).to match([{ id: champ.id }.merge(attributes(champ, value))])
         end
       end
     end
@@ -184,4 +184,10 @@ RSpec.describe PrefillParams do
   def find_champ_by_stable_id(dossier, stable_id)
     dossier.champs.joins(:type_de_champ).find_by(types_de_champ: { stable_id: stable_id })
   end
+
+  def attributes(champ, value)
+    TypesDeChamp::PrefillTypeDeChamp
+      .build(champ.type_de_champ)
+      .transform_value_to_assignable_attributes(value)
+  end
 end
diff --git a/spec/models/types_de_champ/prefill_epci_type_de_champ_spec.rb b/spec/models/types_de_champ/prefill_epci_type_de_champ_spec.rb
new file mode 100644
index 000000000..eecdfdc15
--- /dev/null
+++ b/spec/models/types_de_champ/prefill_epci_type_de_champ_spec.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+RSpec.describe TypesDeChamp::PrefillEpciTypeDeChamp do
+  let(:type_de_champ) { build(:type_de_champ_epci) }
+
+  describe 'ancestors' do
+    subject { described_class.new(type_de_champ) }
+
+    it { is_expected.to be_kind_of(TypesDeChamp::PrefillEpciTypeDeChamp) }
+  end
+  # TODO: SEB describe '#possible_values'
+  # TODO: SEB describe '#example_value'
+
+  describe '#transform_value_to_assignable_attributes' do
+    subject(:transform_value_to_assignable_attributes) { described_class.build(type_de_champ).transform_value_to_assignable_attributes(value) }
+
+    context 'when the value is nil' do
+      let(:value) { nil }
+      it { is_expected.to match({ code_departement: nil, value: nil }) }
+    end
+
+    context 'when the value is empty' do
+      let(:value) { '' }
+      it { is_expected.to match({ code_departement: nil, value: nil }) }
+    end
+
+    context 'when the value is a string' do
+      let(:value) { 'hello' }
+      it { is_expected.to match({ code_departement: nil, value: nil }) }
+    end
+
+    context 'when the value is an array of one element' do
+      let(:value) { ['01'] }
+      it { is_expected.to match({ code_departement: '01', value: nil }) }
+    end
+
+    context 'when the value is an array of two elements' do
+      let(:value) { ['01', '200042935'] }
+      it { is_expected.to match({ code_departement: '01', value: '200042935' }) }
+    end
+
+    context 'when the value is an array of three or more elements' do
+      let(:value) { ['01', '200042935', 'hello'] }
+      it { is_expected.to match({ code_departement: '01', value: '200042935' }) }
+    end
+  end
+end
diff --git a/spec/models/types_de_champ/prefill_type_de_champ_spec.rb b/spec/models/types_de_champ/prefill_type_de_champ_spec.rb
index 52508be91..7477b3789 100644
--- a/spec/models/types_de_champ/prefill_type_de_champ_spec.rb
+++ b/spec/models/types_de_champ/prefill_type_de_champ_spec.rb
@@ -28,6 +28,12 @@ RSpec.describe TypesDeChamp::PrefillTypeDeChamp, type: :model do
       it { expect(built).to be_kind_of(TypesDeChamp::PrefillDepartementTypeDeChamp) }
     end
 
+    context 'when the type de champ is a epci' do
+      let(:type_de_champ) { build(:type_de_champ_epci) }
+
+      it { expect(built).to be_kind_of(TypesDeChamp::PrefillEpciTypeDeChamp) }
+    end
+
     context 'when any other type de champ' do
       let(:type_de_champ) { build(:type_de_champ_date) }
 
@@ -92,4 +98,12 @@ RSpec.describe TypesDeChamp::PrefillTypeDeChamp, type: :model do
       it { expect(too_many_possible_values).to eq(false) }
     end
   end
+
+  describe '#transform_value_to_assignable_attributes' do
+    let(:type_de_champ) { build(:type_de_champ_email) }
+    let(:value) { "any@email.org" }
+    subject(:transform_value_to_assignable_attributes) { described_class.build(type_de_champ).transform_value_to_assignable_attributes(value) }
+
+    it { is_expected.to match({ value: value }) }
+  end
 end